Geological recognition and potential analysis of D block

. Under the guidance of petroleum geology, on the basis of in-depth understanding of the geological characteristics of D block such as structure and sedimentation and the law of oil and gas enrichment, this paper discusses the reservoir potential of D block and selects the target block. The study shows that D block is a fault nose structure controlled by reverse normal fault, and the fault has a controlling effect on its provenance, reservoir formation and oil and gas distribution.


Overview
D block of Huhe noren oilfield is located in beirsumu, new balhu Right Banner, Hulunbuir League, Inner Mongolia Autonomous Region.The structural location belongs to huhe-9 structure of Beixi sub sag and noren structure in Beier Sag of beierhu depression, Hailar Basin, and it is the southward extension of B fault block.The main target horizons are N and X Formation.

Geological recognition of D block 2.1 Structural characteristics
The Hohhot noren structural belt is located in the southwest of Beier Sag and distributed in NE direction.It is a fault nose structure developed under the control of the main control normal fault F1 extending in nee direction and falling to the West.The Nantun Formation was a complete structural belt during the sedimentary period, and the main ontrol normal fault F2 extending NE in the later period cut the structure into two blocks D and B.The fault offsets of both F1 and F2 faults increase from southwest to northeast.All faults in D fault block are normal faults, and most of them are reverse faults.Among them, the main control fault F1 is a reverse growth fault extending to the basement, the main body is shovel type, gradually changing to a seat type with steep upper and lower parts and gentle middle in the East, with large scale and long development time.The extension length in the study area is 8.9km, the fault displacement gradually decreases from west to East, with a maximum of 400m, strike nee, NW tendency and an inclination of 51°; The extension length of fault F2 in the study area is 4.4km, the maximum fault displacement is 60m, the strike is ne, the dip angle is 55°, and the dip is NW.
Secondary small faults are developed in the area, mainly in NE direction, which are normal faults, most of which are reverse faults, with poor inheritance; On the plane of Nantun Formation, it mainly intersects with the main control fault in an oblique way, and on the section, it presents a ladder like, Y-shaped or anti-y-shaped combination; The zhixing'anling formation is mainly parallel to the main control fault in plane.

Stratum sedimentation
The basement of Hailar Basin is Paleozoic and pre Paleozoic strata, and its sedimentary cover is Mesozoic Cretaceous and Cenozoic Neogene and Quaternary strata.The maximum thickness of sedimentary rock is about 6000m, and the main oil bearing series is Lower Cretaceous strata.At present, the sedimentary strata of Hailar Basin are divided into 6 groups and 10 lithologic sections.The main target horizons are N and X Formation.N Formation in D3 block of Huhe Noren oil field is mainly fan delta facies deposit in nearshore shallow water environment.Deposits formed by the traction hydrodynamic mechanism are more common, and the proportion of deposits formed by the gravity hydrodynamic mechanism is relatively small, which indicates that the hydrodynamic conditions in this area have both traction flow and gravity flow, and the occurrence of deposits is the result of the combined action of the two hydrodynamic forces, of which the traction hydrodynamic force occupies a dominant position.There are two sedimentary cycles developed from top to bottom in N Formation of D block.According to the characteristics of sedimentary cycles, two oil-bearing groups I and II are divided.Oil layer group I is mainly composed of thick sandy conglomerate, mudstone and transitional lithology, and the bottom is divided by low resistivity and high gamma thin sand mudstone interbedding and the middle oil layer group; The resistivity curves of II oil layer group are mostly wide, slow and sharp peaks, and the natural gamma is slightly higher than that of the upper oil layer group.The horizontal distribution of strata in D block is characterized by gradual thinning from east to west and annihilation.Reservoir group II is annihilated in the west of D3 well block, and reservoir group I is missing near D8 well block.The N Formation oil layer of D block is developed with glutenite, with a thickness of 39.2 ~ 61.5m and an average thickness of 52.3m.The plane distribution of glutenite is controlled by the distribution of sedimentary fans and topography.The thickness of sandy conglomerate is large in the main body of fan delta and the thick part of stratum sedimentation.On the whole, the thickness of sandy conglomerate gradually thins from north to south.Sandstone in the East and west well areas is mainly developed, and sandstone in well bay D7 of oil formation II.The sandstone of oil formation II is more developed than that of oil formation I, with good continuity and large single-layer thickness.The reservoir lithology of X formation in D block is mainly basalt and pyroclastic rock, which is thick layered, and the thickness of basalt stratum is relatively stable.
According to the research on the volcanic rock reservoir in X, Hohhot Norren area, basalt is of volcanic fissure eruption origin.The magma overflows the surface along the fault and covers the unconformity surface of the lower stratum, forming a flood basalt sheet with a wide distribution, relatively gentle occurrence, relatively stable thickness and composition.Volcanic clastic rocks are developed on the flanks and local top surfaces of the lava sheet.Lithofacies are vertically divided into three parts: overflow facies dense basalt, rock flow self clastic rock and pyroclastic sedimentary rock.A total of 24 wells in D block are drilled into the X formation, and sandstone is developed in all the wells.Due to the influence of drilling depth, the thickness of sandstone varies greatly, with the maximum thickness of 124m, the thinnest only 4m, and the average thickness of 41.6m.According to the seismic attribute analysis, sandstone is generally developed in D block, and the thickest is developed in D8 well block.

Reservoir type
During the sedimentation period of the N Formation of the Beixi sub sag, fan delta deposits of east and west provenances are developed.The well area is generally located in the fan delta front facies belt, and the underwater distributary channel sand bodies of multiphase front are developed.The sand bodies are distributed in a wide range and are staggered, providing a good reservoir space for oil and gas accumulation.In the early stage of the Bexi sub sag, NEE trending faults controlled the formation and distribution of structural belts, while NE trending faults controlled the formation of local structures.The distribution of oil and gas is controlled by NEE and NE trending faults, and it is most abundant at the structural highs.The lithology in the area near the trough also controls the reservoir to a certain extent.
There are three types of oil-water distribution in the vertical direction of N Formation in well block D3: oil layer dry layer water layer, oil layer water layer and oil layer dry layer.The above oil is mainly distributed in the lower dry layer.The oil reservoirs of N Formation are mainly glutenite reservoirs controlled by reverse normal faults, which are lithologic structural reservoirs mainly controlled by structures.The logging curve of high-yield wells in N Formation is box shaped, with a resistance of more than 15 Ω. m and a density of less than 2.4 g/cm 3 , which is a typical underwater distributary channel feature.High yield wells are distributed at the structural high point of the pinch out line of the 15 and 111 layers in the II oil formation of the South Second Member.For example, the effective thickness of D66 drilling is 42.6m, and only 5.9m is effective for shooting.At the initial stage, the daily oil salvage is 3.3t, and the cumulative oil production is 4660t.X oil layer in D block is mainly distributed in upper oil and lower dry, with local upper oil and lower water.Oil and gas are mainly concentrated in the structural highs near the two overlapping lines that are not developed in the strata of N Formation.Because of long-term exposure to the surface, weathering, and local holes and fractures, it is an unconformity reservoir controlled by unconformity.Oil testing and production of high-yield wells are all in Well Block D8.Well Blocks D12 and D3 have overlying formation of the second section of the south, and the fractures and caves at the top of the X Mountains are poorly developed.Oil and gas are enriched and high-yield only near local high point faults.For example, the fault on the west side of D68 controls the formation of local structural high point oil and gas enrichment, which is put into production by conventional shooting.At the initial stage, the daily oil production is 6.3t, and the cumulative oil production is 7325t.As the formation in Well Block D8 has been exposed to the surface for a long time, fractures and caves are developed with high production, and fractures and caves are mainly distributed in the structural highs controlled by the overlap line of the upper II oil formation.

Fault control
According to the sand ground ratio and large fault superposition diagram of the South second section of the exploration and evaluation well in Hohhot noren oilfield, the original entrance of block B is the intersection of large faults, and the growing large fault from the north to the West controls the raw material supply of Hohhot noren oilfield.

Potential analysis
By analyzing the oil and gas distribution, structural location and sedimentary facies development in the highyield well area of D block, it is found that the high-yield wells are distributed in the high part of the structure and the sandstone is developed; The well logging of X formation in well D3 area shows no perforation with highyield oil flow.According to the above characteristics, it is found that the sand body of X formation is developed according to the logging interpretation of well D5 in the old well, and it is recommended to shoot the sandstone of X formation in well D5; A potential block is selected in the north of well D3, which is located on the Horst composed of boundary faults and internal small faults.Faults have strong control over Hohhot noren Oilfield: regional large faults control the material supply of Hohhot noren oilfield; Boundary faults control the formation of lithologic structural reservoirs in D and B blocks; The local microstructure controls the distribution of oil and gas in D3 well area, and the high-yield well is located in the rising wall of the fault.The area with good seismic attributes and the high tectonic position of the fault rising wall is the lower potential tapping area.

Fig. 1
Fig. 1 Sand ground raio and fault superposition diagram of Hohhot noren Oilfield B block and D block in Hohhot noren oilfield are lithologic structural reservoirs controlled by the same boundary fault.The oil layer of N Formation in D block is vertically divided into two sets of oil-water systems.Oil group I is oil layer dry layer, and oil group II is oil layer water layer dry layer.The oil bottom elevation is -567.8~-785.53m,and the oil bottom elevation of well D7 is the lowest.The high-yield well in well D3 area is located at the high part of the fault structure,Well D6 is located at the rising wall of graben.

Table 1
Sandstone Data Statistics of N Formation in D Block Block D and block B are separated by faults, which are fault nose structures under the common control of two boundary faults; The main control fault F1 is a reverse growth normal fault with large scale and long activity time.Its main body extends to the basement in a shovel type and turns into a seat fault with steep upper and lower parts and gentle middle in the East; Small faults are developed in the block, all of which are normal faults, most of which are reverse faults, with small fault displacement and poor inheritance.Two oil formations I and II are developed in N Formation of D block, and the bottom stratum is missing; From east to west, the sedimentary thickness of the strata gradually thinned to extinction.Sandstone of X formation is widely developed, among which well bay D is the most developed.