Distribution characteristics and main controlling factors of oil and gas in Yakela-Luntai oil and gas area

Ma Huiming, Yang Hong, Wang Meiling, Li Guozheng

(Urumqi 8300 1 1, Planning and Design Institute of Northwest Petroleum Bureau)

Yakela-Luntai block is one of the most important oil and gas accumulation areas in Tarim Basin, with 3 oil and gas fields 13, 6 oil-bearing structures and 50 oil and gas reservoirs discovered. By systematically studying the reservoir-forming characteristics of oil and gas fields (reservoirs) in the block, the distribution, reservoir types, reservoir-forming period and reservoir-forming mode of oil and gas fields (reservoirs) in the block are summarized, and the understanding of oil and gas distribution law and its main controlling factors in this area is further improved.

Keywords main controlling factors of oil and gas distribution in Yakela-Luntai block of Tarim Basin

Yakela-Luntai Block (Yaluntai Block for short) is located in Shaya Uplift in the north of Tarim Basin, including Yakela Fault Uplift, southern margin of Kuqa Depression, Shaxi and its peripheral areas. It is one of the most important oil and gas accumulation zones in Tarim Basin and the main gas source area of "West-to-East Gas Transmission". The petroleum geological conditions in this block are complex and the exploration degree is high. It is of great significance to study the distribution law of oil and gas in this area, especially for natural gas exploration.

1 oil and gas field (reservoir) distribution map

At present, 13 oil and gas fields have been discovered in Yalun block: Yakela condensate gas field, Yaha oil and gas field, Donghetang oil and gas field, Yingmai No.7 oil and gas field, Hongqi oil and gas field, Yingmai 1 oil field, Yingmai No.2 oil and gas field, Yangtak 1 condensate gas field, Yangtak No.5 oil field, Yudong No.2 oil and gas field, Tiergen condensate gas field and six oil-bearing fields. Lunxi 1 (Well Lunxi 1-O), Tuohula 1 (Well Sha53 AnZ Natural Gas), Yaha 2-3 (N2k) and Lunbei Ti3 (Well K2-E).

Accumulated proven geological reserves: oil 5822.4× 104t, dissolved gas 65.88× 108m3, natural gas 930.69× 108m3, condensate oil 3894.78× 104t, and total oil-gas equivalent/kloc-0.

Controlled geological reserves: oil 3747× 104t, dissolved gas 65.88× 108m3, natural gas 386.74× 108m3, condensate oil 6 10.2× 104t, with a total oil-gas equivalent of 8855.

1. 1 plane distribution map of oil and gas fields (reservoirs)

The oil and gas reservoirs in the work area of Yalun block are mainly distributed in the local structural belt controlled by large faults, and are concentrated in the following four areas in the plane: the southwest edge of Yakela fault convex (Hongqi, Donghetang-Yakela), the south edge of Kuqa depression (Yaha-Qiuli-Qunbaketai 2 well), the northwest of Shaxi uplift (Yudong-Yangtak-Yingmai 7) and the Luntai area in the middle of Yakela fault convex.

Figure 1 Oil and Gas Distribution Map of Yakela-Luntai Block 1 Oil and Gas Distribution Map of Yakela-Luntai Oil and Gas Belt

1- registration block; 2- Reservoir; 3- gas reservoir; 4- drilling; 5- Intrusive rock mass; 6- Fault; 7- Petroleum System

1.2 vertical distribution of oil and gas fields (reservoirs)

Oil and gas reservoirs and industrial oil flows have been found in the pre-Sinian, Sinian, Cambrian, Ordovician, Carboniferous, Jurassic and lower Cretaceous Kapshaliang Formation, upper Cretaceous-Paleogene, Miocene Suweiyi Formation and Pliocene Kuche Formation 10 (Table 1 and Figure 2), and there are vertical faults and gas flows.

Table 1 Reserves Distribution Table of Different Layers in Yakela-Luntai Oil-bearing Area of Yalun Block 1

Fig. 2 Distribution of oil and gas reserves in different horizons of Yakela-Luntai 2 Distribution of oil and gas bearing zone in Yakela-Luntai

1.2. 1 Pre-Mesozoic

Oil and gas are mainly distributed in Cambrian-Ordovician and Lower Carboniferous. The Cambrian-Ordovician is dominated by buried hill reservoirs, and the reservoirs are carbonate rocks. The Lower Carboniferous is dominated by compressional anticline reservoirs, and the reservoir is Donghe sandstone. Oil and gas resources are mainly crude oil, followed by condensate gas. Other horizons have smaller reserves. The lateral distribution of oil and gas in the pre-Mesozoic strata in this block is as follows: (1) Pre-Sinian system (AnZ): At present, industrial natural gas flow is only found in Tuohula area at the western end of Yakela fault convex. Well Sha 53 is located in Tuohula 1 structure. In March 1998, DST test was carried out in the fractured reservoir of pre-Sinian metamorphic monzonite, and industrial gas flow was obtained. Natural gas 10870m3/d, with trace oil. According to the volumetric method, it is predicted that the gas reserves of Sinian system before Tuohula 1 structure are 5.29× 108m3.

(2) Sinian system (Z): industrial oil and gas abortion in Yaklasha 4 well, with daily oil production of 13.32 m3 and gas production of 12× 104m3, which is produced in dolomite interval 5465438 ~ 5428. 19m in the middle of Sinian system. This "gas reservoir" may be a large gas reservoir with unconformity bottom water.

(3) Cambrian (): industrial oil and gas aborted in Yaklasha 7 well.

(4) Ordovician (O): Lower Ordovician condensate gas reservoir in Yakela, Lower Ordovician gas reservoir in Yingmai No.7 oil and gas field, Lower Ordovician gas reservoir in Yingmai 1 and Yingmai No.2 structure, and Cambrian-Ordovician condensate gas reservoir in Yaha 5 ~ 7 well area in Yaha oil and gas field.

(5) Carboniferous (C): Lower Carboniferous oil and gas field in Donghetang.

1.2.2 Mesozoic and Cenozoic

Oil and gas are mainly distributed in the Lower Cretaceous Kapshaliang Formation, the Upper Cretaceous-Paleogene and Miocene Suweiyi Formation. The Lower Cretaceous Kapshaliang Formation is dominated by compressional anticline oil and gas reservoirs, and the reservoir is mainly the bottom block sandstone of Lower Cretaceous Kapshaliang Formation. Upper Cretaceous-Paleogene and Miocene Suweiyi Formation are mainly faulted anticline reservoirs, and the reservoirs are mainly Suweiyi Formation and Upper Cretaceous-Paleogene sandstone with good physical properties and large thickness. Mesozoic and Cenozoic oil and gas reservoirs were formed in Himalayan period. The type of oil and gas resources is mainly condensate gas, with a small amount of crude oil. The lateral distribution of Mesozoic and Cenozoic oil and gas in this block is as follows:

(1) Jurassic (J): Jurassic gas reservoirs in Well Yaklasha 4 and Well Sha 7.

(2) Lower Cretaceous Kapshaliang Formation (K 1kp): Yakela Lower Cretaceous condensate gas reservoir, Donghetang Lower Cretaceous gas reservoir and Lunxi 1 Lower Cretaceous gas reservoir.

(3) Upper Cretaceous Paleogene (K2-E): Tiergen, Luntai, Yudong 2, Yangta 1 and Yangta 2 Upper Cretaceous Paleogene-condensate gas reservoirs; Upper Cretaceous-Paleogene reservoirs of Yangta 5 and Yingmai 9.

(4) Miocene Suweiyi Formation (N 1s): Yaha, Hongqi, Tiergen, Yingmai No.7 and Qunbak (well Tai 2) condensate gas reservoirs.

(5) Pliocene Kuqa Formation (N2k): YH303 of Yaha No.2 and No.3 structures was tested for industrial oil flow in June195+0015 ~16 at the interval of 273 1.2 ~ 2850.54 m, with daily production.

1.3 offshore and onshore oil and gas distribution and petroleum system division

Because there are two oil sources in the Yalun block, oil and gas can be divided into two types according to the origin: one is marine oil and gas with sapropelic kerogen as the source rock, and the other is continental oil and gas with sapropelic kerogen as the source rock. Marine oil and gas are mainly distributed in the south of the block, along the Luntai fault-Southwest Shaanxi line, and mainly distributed in Paleozoic (O 1, C 1) and Mesozoic (K 1kp), mainly in compression anticline reservoirs (Upper Paleozoic and Mesozoic) and buried hill reservoirs (Lower Ordovician). Continental oil and gas are mainly distributed in the north-central part of the block, roughly north of Yingmaiqi-Hongqi-Tuohula-Yaha-Luntai line. Oil and gas are mainly distributed in Cenozoic (N 1 s, K2-E), followed by Lower Paleozoic (O 1), mainly distributed in fault anticlines and buried hills (O 1).

According to the distribution characteristics of oil and gas in this area and its relationship with source rocks, combined with the research results of the Ninth Five-Year Plan, this block can be divided into two oil-bearing systems: the northern continental oil-bearing system and the southern marine oil-bearing system. The marine petroleum system is distributed in the southern margin of the block, with Yingmai 1, 2- Donghetang-Yakela-Lunxi 1 along the line, and the northern part of the block belongs to the continental petroleum system. At the junction of the two systems, there is a certain degree of mixing of terrigenous and marine oil and gas, such as the Lower Ordovician of Yingmai 7, Sinian before Pintosala 53 well and Lunxi 1. Marine oil and gas are mainly produced in Mesozoic and Paleozoic, while terrestrial oil and gas are produced in Cenozoic and Lower Paleozoic. These two petroleum systems have the following basic characteristics:

1.3. 1 Southern Offshore Oil System

The source rocks are CAMBRIAN-Ordovician marine carbonate rocks and argillaceous rocks with low organic matter abundance, and the parent material type is sapropelic, with Hercynian as the main oil generation period and Himalayan as the "secondary" oil generation period. The reservoirs are carbonate rocks of Lower Paleozoic, Donghe sandstone of Lower Carboniferous and bottom block sandstone of Kapshaliang Formation of Lower Cretaceous. Part of Lower Paleozoic carbonate reservoirs. The caprocks are mainly limestone and calcareous mudstone of Upper Ordovician, mudstone of upper part of Lower Carboniferous and mudstone of middle and upper part of Kapshaliang Formation of Lower Cretaceous. The trap types are anticline trap and buried hill trap. Oil and gas resources are mainly crude oil, followed by condensate gas. Oil and gas mainly migrate from south to north along the regional unconformity. Conditions for oil and gas preservation The early Shaxi reservoir is less affected by multi-stage tectonic movement, and the conditions for eastward preservation are better. Oil and natural gas have the following basic characteristics:

The composition of (1) light hydrocarbons is characterized by high n-alkanes and low cycloalkanes, with MCH < 45%.

(2) Cycloalkanes in saturated hydrocarbons are higher than alkanes, and the rest are alkanes and phytoalkanes. The range of w(Pr)/w(Ph) is 0.80 ~ 1.20.

(3) Aromatic hydrocarbons are rich in high sulfur aromatics.

(4) Isotope distribution is rich in light carbon isotopes and heavy sulfur isotopes, with δ 13C ranging from-31‰ to-34 ‰, sulfur isotope δ 34s > 15 ‰ and aromatic hydrocarbon δ 13c >-30 ‰.

(5) Biomarker compounds are characterized by being rich in long-chain tricyclic terpanes.

(6) The absolute content of trace metal elements in crude oil is high, with V reaching n× 10-5 and Ni reaching N× 10-6 (Ordovician crude oil S 13, S 16, YM 1), W.

(7) The maturity of crude oil is mainly high maturity.

(8) Shaxi crude oil in the west has undergone strong water washing oxidation degradation, and the light hydrocarbon water washing index TOL <10; Rich in metal vanadium and nickel.

1.3.2 northern continental petroleum system

The source rocks are Triassic-Jurassic argillaceous rocks and coal measures strata in Kuqa depression, with high organic matter abundance, humic type as the main parent material and Himalayan period as the main oil generation period (Paleogene entered the hydrocarbon generation period and Neogene reached the peak of hydrocarbon generation). The reservoir is mainly sandstone of Upper Cretaceous-Paleogene Suweiyi Formation, with good physical properties and large thickness. Some carbonate reservoirs of Lower Paleozoic and fractured reservoirs of metamorphic rocks of Pre-Sinian system. The caprocks are mainly mudstone of Jidike Formation, mudstone of middle Suweiyi Formation, mudstone of Upper Cretaceous-Paleogene and mudstone of Lower Cretaceous. The trap type is mainly faulted anticline, and the formation period is Himalayan. And buried hill traps. The type of oil and gas resources is mainly condensate gas, with a small amount of crude oil. Oil and gas mainly migrate from north to south along the good reservoir (diversion layer) under the regional caprock (N 1j) and the Archaean surface layer, and the oil and gas preservation conditions are good. Oil and natural gas have the following basic characteristics:

(1) is mainly condensate oil, characterized by high wax (> 10%), high freezing point (> 20℃) and low sulfur (< 0.5%), and the density is generally less than 0.9g/cm3.

(2) The composition of light hydrocarbons is characterized by low n-alkanes and high cycloalkanes, with MCH > 45%.

(3) Among saturated hydrocarbons, alkanes are more than cycloalkanes, which has obvious advantages of alkanes, and PR/pH is greater than 1.5.

(4) Isotope distribution is rich in heavy carbon isotopes and light sulfur isotopes, δ 13C is generally > -30 ‰, sulfur isotope δ34S is generally < 10% ‰, and aromatic hydrocarbon δ 13C is generally.

(5) The biomarker lacks tricyclic terpanes, which can detect γ -paraffin and Olian.

(6) The absolute content of trace metal elements in crude oil is low, all below 0. 1× 10-6, and it is poor in vanadium and rich in nickel, w (V)/w (Ni) < 1.

(7) Low maturity.

(8) The epigenetic change of crude oil is small, and the light hydrocarbon washing index TOL is 30 ~ 50.

1.4 Types and distribution of oil and gas resources

The types of oil and gas resources in Yalun block are crude oil and condensed gas. The oil and gas reserves are equivalent, and the gas is slightly more.

1.4. 1 crude oil

They are mainly distributed in the Cambrian-Ordovician of Yaha No.5 and No.7, the Lower Ordovician of Yingmai 1, Yingmai No.2 and Yingmai No.7, the Paleogene of Upper Cretaceous of Yingmai No.9, the bottom sand of Yaha 1, Hongqi 1 Miocene Suweiyi Formation, and the Lower Carboniferous and Lower Cretaceous Kafu of Donghetang. Geological reserves: crude oil 936 1.4× 104t, dissolved gas10.18×108m3, total oil and gas equivalent14000.74×/kloc-0.

1.4.2 condensate gas

35 widely distributed condensate gas reservoirs have been discovered in the whole block. Geological reserves: natural gas1317.43×108m3, condensate oil 4504.98× 104t, total oil and gas equivalent19131.34.

Two types of oil and gas reservoirs

The oil and gas reservoirs in this area can be divided into three types: structural oil and gas reservoirs, stratigraphic oil and gas reservoirs and lithologic oil and gas reservoirs.

2. 1 structural oil and gas reservoir

It is the main oil and gas reservoir type in Yalun block, and is further divided into anticline structural oil and gas reservoirs and fault oil and gas reservoirs.

2. 1. 1 anticline oil and gas reservoir subclass

According to the causes of anticlines, they can be subdivided into three types: compression anticlines, fault anticlines and detachment anticlines.

Compressive anticline oil and gas reservoirs: Lower Cretaceous gas reservoir in Yakela condensate gas field, Carboniferous gas reservoir in Donghetang oil and gas field, Upper Cretaceous-Paleogene gas reservoir in Yingmai No.9 oil and gas field, and Upper Cretaceous-Paleogene condensate gas reservoir in Yudong No.2, etc.

Faulted anticline oil and gas reservoirs: almost all anticline oil and gas reservoirs in Yalun block are accompanied by faults, which have different degrees of control over oil and gas reservoirs. Fault anticline oil and gas reservoir refers to a semi-anticline formed by a fault passing near the axis of the anticline or one wing of the anticline being cut by a fault, and the fault is one of the main controlling factors of this kind of oil and gas reservoir. It is the main reservoir type of Cenozoic in this block, and almost all the top and bottom sandstone reservoirs of Upper Cretaceous-Paleogene and Miocene Suweiyi Formation belong to this type, which is a major feature of Yalun block. Specifically, it has the following characteristics: oil and gas reservoirs are all developed in the north wall (footwall) of NNE-trending and EW-trending south-dipping normal faults with large dip angles, mostly between 50 and 70. Thick mudstone and gypsum-bearing mudstone of Jidike Formation in the south panel (upper panel), mudstone and gypsum-bearing mudstone in the middle of Miocene Suweiyi Formation, mudstone, rock salt and gypsum in the middle and upper part of Upper Cretaceous-Paleogene, blocking the sandstone at the top and bottom of Miocene Suweiyi Formation in Wan, and sandstone of Upper Cretaceous-Paleogene, forming a fault anticline trap.

Detached anticline reservoir: Lower Ordovician reservoir in Yingmai No.2 oil and gas field.

2. 1.2 fault reservoir subclass

Fault nose oil and gas reservoir: the upward direction of nose structure is formed by fault cutting, such as Lunxi 1 Lower Cretaceous Kapshaliang Formation oil reservoir.

2.2 Reservoir

(1) monoclinic buried hill reservoir. Yakela Lower Ordovician condensate gas reservoir.

(2) Dissolved unconformity reservoir. Cambrian gas reservoir in Yaklasha 7 well and Ordovician gas reservoir in Yingmai 7 well.

2.3 Lithologic oil and gas reservoirs

There are sandstone lenticular reservoirs and fractured reservoirs in Yalun block, and the latter is classified into this category because its reservoir is determined by the change of reservoir performance.

(1) sandstone lenticular reservoir. Jurassic "gas reservoir" in well Sha 7 of Yakela condensate gas field.

(2) Fractured reservoirs. Tuohula 1 Structure (Well Sha 53) Pre-Sinian metamorphic fractured gas reservoir.

3 reservoir-forming period

There are two main oil and gas accumulation periods in Yalun block: late Hercynian period and Himalayan period, of which Himalayan period is the most important. This is determined by the two main oil-generating periods of Late Paleozoic and Cenozoic in northern Tarim and the two main tectonic movements of Late Hercynian and Himalayan in this area.

3. 1 Late Hercynian reservoir-forming period

Yingmai 1 and Lower Ordovician No.2 reservoirs are the representatives of this period. Donghetang Lower Carboniferous oil and gas fields were formed in the late Hercynian-Indosinian period, all of which belong to marine reservoirs, and the traps are mainly Paleozoic insider anticline structures. It is characterized by a complete reservoir-cap assemblage in Paleozoic, traps formed by Caledonian-Hercynian folds, and oil and gas accumulation generated by Cambrian-Ordovician source rocks in the same period. Planarly, it developed in the southwest of Aaron Block, with relatively little Paleozoic denudation, in the south of Shaxi Uplift, in the north of Halahatang Depression and in the southwest of Yakela Fault Uplift.

3.2 Himalayan reservoir-forming period

Most of the oil and gas reservoirs in the Yalun block are the products of this period, with a wide range of oil and gas producing layers, including Pre-Sinian, Cambrian-Ordovician, Lower Cretaceous Kapshaliang Formation, Upper Cretaceous-Paleogene, Miocene Suweiyi Formation and Pliocene Kuqa Formation. The resource structure is dominated by natural gas, and both land and sea sources of oil and gas are developed. Planarly, Cenozoic oil and gas reservoirs (including Upper Cretaceous-Paleogene) are distributed in the whole region. Mesozoic oil and gas reservoirs are mainly distributed in the western segment of Luntai fault, Donghetang-Yakela-Lunxi 1 zone; Pre-Mesozoic oil and gas reservoirs are distributed in Shaxi, Yakela, Yaha and Tuohula in the central and western part of the block. This reservoir-forming period is characterized by late trap formation, oil and gas are the product of Himalayan period, fault anticline oil and gas reservoirs are the main ones in Cenozoic, and compressional anticline oil and gas reservoirs in Mesozoic. The pre-Mesozoic oil and gas reservoirs formed in Himalayan reservoir-forming period are mostly related to unconformity, and there are ① many trap types: monoclinic buried hill, denudation unconformity, fractured body, detachment anticline and so on. ② The pre-Mesozoic was weathered and denuded for a long time, and the reservoir developed near the weathered surface, with no cap rock or incomplete cap rock conditions. Only in the Mesozoic era, especially in the Cretaceous period, the corresponding caprock conditions were formed, and the oil storage trap was formed. (3) Triassic, Jurassic terrestrial oil and gas and Lower Paleozoic Cambrian-Ordovician source rocks in Kuqa Depression in Himalayan period generated oil, and oil and gas gathered in the above traps to form reservoirs.

In addition, Yingmai No.7 Lower Ordovician dissolution unconformity reservoir was formed in the late Yanshanian-early Himalayan period.

4 Reservoir-forming model

According to the source rocks, pay zones and reservoir-forming stages of the block oil and gas reservoirs, the Yalun block is divided into four reservoir-forming models: Paleozoic ancient reservoirs, epigenetic ancient reservoirs, Cenozoic ancient reservoirs and Cenozoic new reservoirs.

4. 1 Paleozoic ancient reserve

Marine Lower Paleozoic Cambrian-Ordovician source rocks generated oil in Paleozoic (Paleozoic), accumulated in Paleozoic clastic rocks and carbonate reservoirs (ancient reservoirs), and formed reservoirs in Paleozoic. Distributed in the southern offshore oil system. Since the late Caledonian, Cambrian-Ordovician source rocks began to generate oil, reaching the peak of oil generation in the early and middle Hercynian, and oil and gas accumulated in Paleozoic. The trap types are mainly Paleozoic large-scale insider anticlines, which are mainly distributed in the south-central part of Shaxi uplift, such as Yingmai 1, Yingmai 2 Lower Ordovician reservoir and Yudong 2 Lower Ordovician reservoir. In this area, the extremely thick asphalt sandstone (ancient reservoir) of Ketuer Shengli 1 well also belongs to this category.

4.2 Supergene Paleo-oil Reservoir

The marine lower Paleozoic Cambrian-Ordovician source rocks generated oil (epigenetic) in late Cenozoic, and formed reservoirs in Paleozoic clastic and carbonate reservoirs (paleo-reservoirs) and Mesozoic clastic reservoirs, and formed reservoirs in Cenozoic. Distributed in the southern offshore oil system. After the late Hercynian period, due to the large-scale uplift and erosion in the region, after the Yanshanian period, with the deposition of Mesozoic and Cenozoic, the Cambrian-Ordovician source rocks were buried deep to the threshold of oil generation and generated oil for the second time. Oil and gas reservoirs are formed in Paleozoic, and the trap types are mainly Paleozoic buried hills and insider anticlines. It is mainly distributed in the south of Yakela fault convex, and the reservoirs of Lower Ordovician, Lower Cretaceous Kapshaliang Formation, Lower Carboniferous in Donghetang, Lower Cretaceous Kapshaliang Formation and Lunxi 1 belong to this category.

4.3 Newborn Ancient Reserve

The terrestrial Triassic-Jurassic in Kuqa depression is a source rock, which generated oil (newborn) in Himalayan period, and oil and gas accumulated in Paleozoic and older strata. Oil and gas mainly migrated southward along the integration surface and accumulated in Paleozoic carbonate reservoirs and pre-Sinian fractured reservoirs under the unconformity surface. Petroleum system distribute in that northern mainland. Yingmai 7 Lower Ordovician reservoir, Yaha 5 ~ 7 Lower Ordovician reservoir and Tuohula 1 (well Sha 53) Pre-Sinian gas reservoir all belong to this category.

4.4 Freshmen and new reserves

The terrestrial Triassic-Jurassic in Kuqa depression is a source rock, which generated oil (regenerated) in Himalayan period. Oil and gas are accumulated in Cenozoic clastic reservoirs, mainly Miocene Suweiyi Formation and Upper Cretaceous-Paleogene. Petroleum system distribute in that northern mainland. All Cenozoic oil and gas reservoirs in Yalun block belong to this category.

5 Main control factors of oil and gas distribution

5. 1 The two major oil and gas source areas in the north and south provide abundant oil and gas resources, control the distribution range of oil and gas, and have sufficient oil and gas supply. Formed two major oil and gas systems: ocean and land.

5.2 Late Paleozoic-Mesozoic long-term paleouplift and Cenozoic continuous monoclinic upwarping regional structures become the long-term migration direction of marine oil and gas.

This area has experienced multi-stage tectonic movement. After the Tarim movement, the Sinian-Cambrian platform deposits with different thicknesses were generally accepted in northern Tarim. In the middle Caledonian period, the folds in this area were uplifted, forming Yakela fault uplift controlled by luntai fault, which caused the Cambrian-Ordovician system to suffer from different degrees of erosion, with a large uplift in the northeast, and most areas of Sinian-Ordovician system were missing. From the late Caledonian to the early Hercynian, this area is still an inherited uplift. Silurian-Devonian deposits are only accepted in the southwest and overlap in the uplift direction. After that, it accepted the superimposed deposition of Carboniferous-Permian. The late Hercynian tectonic movement led to the regional uplift of the whole northern Tarim area, and the strata were generally eroded. During Indosinian period, the area continued to uplift, which was the direction of oil and gas migration in the early Cambrian-Ordovician of Lower Paleozoic. By the Yanshanian period, this area began to decline and accept deposition. Himalayan tectonic movement caused the southern part of the area to rise, and the Kuqa depression in the northern part to fall sharply, and a huge Cenozoic era was deposited. In Mesozoic and Cenozoic, a monocline inclined to the north was formed. Oil and gas reservoirs were formed in Triassic-Jurassic continental oil and gas in Kuqa depression in the north and Cambrian-Ordovician Himalayan oil and gas in the south.

5.3 The late trap formation period and oil and gas generation period determine that most of the oil and gas in this block are late reservoir formation.

5.4 Reservoirs and their lateral changes are important determinants to control the geological horizon and plane distribution of oil and gas.

5.4. 1 Aaron's main reservoirs are Lower Ordovician, Lower Carboniferous, Lower Cretaceous Kapshaliang Formation, Upper Cretaceous-Paleogene and Miocene Suweiyi Formation, and almost all oil and gas geological reserves have been found in these horizons.

5.4.2 The plane distribution and sedimentary facies of reservoirs in each era determine the distribution of oil and gas reservoirs.

(1) Lower Paleozoic carbonate reservoirs are mainly distributed on both sides of Yakela fault convex and Shaxi area, so CAMBRIAN-Ordovician formed oil and gas fields (reservoirs) in Yaha 5 ~ 7 and Lower Ordovician in Yakela, Yingmai 7, Yingmai 1 and Yingmai 2. The Lower Carboniferous of Upper Paleozoic is distributed in the southwest margin of Yakela Fault Convex, the north of Halahatang Depression and the south of Shaxi Uplift, forming oil and gas reservoirs in Donghetang area.

(2) The sandstone at the bottom of Lower Cretaceous Kapshaliang Formation in Mesozoic is deposited in the fan delta plain of Yakela-Donghetang and Luntainan, with good reservoir conditions and oil and gas accumulation. The condensate gas reservoirs of Lower Cretaceous Kapshaliang Formation in Yakela, Lower Cretaceous Kapshaliang Formation in Donghe 1, Lower Cretaceous Kapshaliang Formation in Donghe 23 and Lunxi 1 have been discovered.

(3) The Upper Cretaceous-Paleogene is the reservoir with the largest thickness and good reservoir properties in the Yalun block. In the middle of the block, the western part of Yakela fault convex (Yaha-Donghetang and the western part) is braided delta front sand flat deposit, in which the upper Cretaceous-Paleogene has the best reservoir properties in the block, and the core analysis porosity of 5437~5474 m interval of Sha 53 well is 6570. The permeability ranges from114×10-3 to 5245×10-3 μ m2, with an average of1321.2×10-2. Moreover, because the trap amplitude and oil and gas column height are mostly braided delta plain deposits in the east of the bottom of Miocene Suweiyi Formation, mudstone and silty mudstone caprocks of 1.5 ~ 30m are developed at the top, forming a local reservoir-cap combination in this area. With the cooperation of structural conditions, two condensate gas fields, Tiergen and Luntai, were formed, and the Ti3 well in the northern part of Tibei structure and the Ti2 well in the northern part of luntai county formed condensate gas reservoirs. The Upper Cretaceous-Paleogene in the northwest of Shaxi Uplift in the west is alternately deposited by salt lakes and sand flats. Large sections of gypsum-bearing mudstone and salt rocks are developed in the middle and upper parts, which form a good reservoir-cap combination with sandstone reservoirs below, forming Yangta 1, Yangta 2, Yangta 5 and Yudong 2 oil and gas reservoirs.

(4) The bottom sand reservoir of Miocene Suweiyi Formation is the most important oil and gas producing zone in Aaron Block, with stable distribution and good reservoir physical properties, which basically inherits the sedimentary characteristics of Upper Cretaceous-Paleogene. The largest number of oil and gas reservoirs were found, and 12 condensate gas reservoir was formed in Yaha, Hongqi, Yingmai 7, Qiuli and Qunbak (well Tai 2).

(5) The top sand reservoir of Miocene Suweiyi Formation is another most important oil and gas producing zone in Aaron Block, with stable distribution and good reservoir performance. The main body of Yakela fault convex in the middle of the block is fan-edge sand flat deposition, and the distribution of oil and gas reservoirs is obviously controlled by it. It has been found that oil and gas reservoirs are mainly distributed in the Yaha-Qiuli-Tiergen line on the north side of Yakela Fault Convex. Yaha, Hongqi, Qiuli, Qunbak (Well Tai 2) and Tiergen form 8 condensate gas reservoirs.

5.5 Faults mainly control the distribution of Cenozoic fault anticline and traction anticline traps, and then control the distribution of oil and gas. Faults are the main factors that block oil and gas in such traps.

The distribution of Allen oil and gas shows that almost all oil and gas reservoirs appear near large faults in the plane, and the highest level of oil and gas reservoirs in the vertical direction is the highest level of these faults. The research shows that the role of faults in the process of fluid migration is changeable and periodic, and faults mainly play a sealing role in the static state and mainly play an opening role in the active period and its short period (Wang Ping,1994; Hipper,1993; Hooper, 199 1). Therefore, faults that are active at the same time as oil and gas migration are mainly used as oil and gas migration channels, and the shielding effect of faults on oil and gas is invalid at this time.

The main time of oil and gas migration in Kuqa Depression (Baicheng Depression and Yangzhen Depression) is since 5Ma, that is, since the deposition of Kuqa Formation (N2k).

Jidike Formation (N 1j) is the latest fault layer in the Cenozoic development of the Allen Block, indicating that its main active time was before the deposition of Kangcun Formation. Therefore, the faults in this area stopped moving before the main period of oil and gas migration in Kuqa depression (since the deposition of Kuqa Formation), which mainly played the role of blocking and shielding oil and gas. Therefore, many faulted anticline reservoirs have been formed in this block. The trap mechanism of faults is mainly Miocene Jidike Formation and Suweiyi Formation thick mudstone and gypsum-bearing mudstone, and Upper Cretaceous-Paleogene thick mudstone, salt rock and fault disk sandstone reservoirs are butted and closed.

Oil and gas distribution and main controlling factors in Yakela-Luntai petroliferous belt

Ma Huiming, Yang Hong, Wang Meiling, Li Guozheng

Planning and Design Institute of Northwest Petroleum Geology Bureau? rümqi 8300 1 1)

Abstract: Yakela-Luntai belt is one of the most important oil and gas enrichment zones in Tarim Basin. At present, 13 oil and gas fields, 6 oil-bearing structures and 50 oil and gas reservoirs have been discovered. Through the systematic study of the formation characteristics of various oil and gas reservoirs, the distribution, types, formation time and formation mode of various oil and gas fields are summarized, and the distribution and main controlling factors of oil and gas reservoirs are correctly understood.

Key words: main controlling factors of oil and gas distribution in Yakela-Luntai belt, Tarim Basin