Characteristics And Main Enrichment Controlling Factors Of Tight Sandstone Gas Reservoir Under The Influence Of Volcanic Activity

The tight sandstone gas resources in the Songliao Basin are very rich and have broad exploration and development prospects.However,due to the strong tectonic and volcanic activities,the accumulation pattern and distribution law of tight sandstone gas reservoirs in this area are not clear,which poses a challenge to the exploration and development of tight sandstone gas.The Dehui depression is located in the south of Songliao basin.It is found that the Baojia Sub-Depression in the east of Dehui depression develops a complex gas reservoir in the first member of Yingcheng Formation,which confirmed that the relationship between volcanic activity and the enrichment of tight sandstone gas reservoir is the key to gas field exploration and development.This thesis takes the tight sandstone gas reservoir under the influence of volcanic activity in the first member of Yingcheng Formation in the Baojia Sub-Depression,Dehui Depression as the research object,Guided by structural geology,reservoir sedimentology and petroleum geology,the core,log,seismic,geochemical data and gas test dynamic data are comprehensively used on the basis of previous studies.In-depth and systematic study of volcanic activity,sequence stratigraphic framework,sedimentary characteristics and reservoir characteristics in the study area,summing up gas reservoir types and distribution rules,defining the main factors of tight sandstone gas accumulation and enrichment,and exploring the correlation between volcanic activity and the development of tight sandstone gas reservoirs,providing references for the exploration and development of tight sandstone gas reservoirs under the influence of volcanic activity.The main conclusions of this thesis are as follows:1.The Yingcheng Formation of Baojia Sub-Depression in Dehui Depression depression experienced two volcanic activities and one magmatic intrusion during its depositional period.The volcanic activities formed rock facies equal to explosive facies and spillage facies.In the early stage of volcanic activity,the spillage facies was the main lava with obvious volcanic channels.In the middle period of volcanic activity,pyroclastic rocks of explosive facies were dominant.The late magmatic intrusion was dominated by intrusion rocks that flowed along early volcanic channels and faults.The efusion facies mainly developed dacite,rhyolite,fused tuff and other lithologies.The logging curve is characterized by a large set of box-type medium-high gamma and medium-low resistivity,and the flow bedding structure or fusion structure can be seen from imaging logging.The seismic response is characterized by strong reflection,which is generally disordered and sub-parallel reflection structure,and its interior is mostly characterized by mound-like weak amplitude.The vertical thickness of the volcanic facies is large.The pyroclastic rocks of explosion facies mainly develop tuff,sedimentary tuff,breccia tuff and other lithology.The logging curve is characterized by micro-tooth high gamma and high resistance,and the imaging logs show obvious sedimentary bedding structure or breccie characteristics.The seismic response is characterized by parallel-subparallel layered reflection.The vertical thickness of the volcanic facies is generally small,but widely distributed.The intrusion facies mainly developed diabase.The logging curve is characterized by a large set of box-type low gamma and high resistivity,and the imaging logging shows the characteristics of massive structure,and the obvious interface with the sedimentary formation can be seen.The seismic response is of medium-strong amplitude and continuous parallel reflection structure.During the period of intrusion,the magma energy is weak,and it is difficult to eject from the surface,and it can only intrude along the fault and sedimentary strata,with a large change in thickness.In the study area,there are mainly two volcanic rock belts distributed along the SW-NE direction:the volcanic belt centered on Well Deshen 17-Well Deshen 7-Well Deshen 83,and the volcanic belt in Well Deshen 111 and its surrounding areas.The former extends to the boundary of the depression,with a larger distribution range.2.The sedimentary strata of Yingcheng Formation in Baojia Sub-Depression of Dehui Depression depression can be divided into six third-order sequences（SQ1～SQ6）.During the sedimentary periods of SQ1～SQ3and SQ4～SQ6,the lacustrine basin expanded to shrink respectively,and SQ3 and SQ6 suffered denuding.In the Baojia Sub-Depression,the sequences from south to north are well developed,and the main sequence interfaces can be traced in the whole region.SQ1 sequence mainly consisting of grey mudstone,tuff-tuff conglomerate and local intrusive rocks,and the thickness is generally thick in the middle and thin on both sides.The SQ2 sequence is mainly composed of gray-black mudstone,tuffaceous siltstone,tuffaceous fine sandstone,and grey conglomerate.The thickness of SQ2 sequence is generally thick in the middle and thin on both sides.The SQ3 sequence Baojia Sub-Depression is widely distributed in the north-south direction,and the distribution range is slightly expanded from the bottom to the top.The main lithology is pyroclastic rock.The logging curve and lithology at the bottom of the sequence change abruptly.Under the interface are gray-black mudstone,tuffaceous glutenite,tuffaceous fine sandstone,and the thickness of the stratum is gradually reduced from south to north.The main lithology of SQ4 is thick gray black mudstone with thin gray coarse sandstone.The main lithology of SQ5 is gray-black mudstone,tuffaceous siltstone,tuffaceous fine sandstone and gray glutenite.The lithology of SQ6 is mainly sandy conglomerate with thin mudstone,and the grain size is significantly coarser than that of SQ4and SQ5.The lower part of SQ6 is characterized by positive rhythm,and gray mudstone is deposited.The upper part is mainly composed of variegated glutenite deposits,and the grain size gradually coarsens from bottom to top.On the plane,the SQ1 has a small sedimentary range and a thin stratum.The SQ2 lake basin expands rapidly,the scope of deep depression area expands,and the step contemporaneous fault controls the development of multiple depression patterns.The SQ3 is relatively small in thickness,and volcanic rocks are widely developed.It is generally subject to denudation,incomplete denudation and serious denudation,and the deep depression area is banded.The SQ4 has a small sedimentary range and a relatively thin stratum.The east is controlled by the Dedong fault,and the west is generally characterized by overlap,which is basically not affected by the fault.The SQ5 lake basin expands rapidly,the scope of deep depression area expands,and the step contemporaneous fault controls the development of multiple depression patterns.The SQ6 is relatively thick,and the top is subject to certain denudation.3.The main sedimentary system type of Yingcheng Formation in the study area is fan delta-lake system,the SQ1～SQ3 and SQ4～SQ6 periods experienced the process of water rising and falling respectively.The rock types of Yingcheng Formation in the study area include glutenite,conglomerate,mudstone,etc.The types of sedimentary facies can be divided into fan delta facies and lacustrine facies,which can be further divided into seven types of sedimentary microfacies,namely,fan delta plain distributary channel,interdistributary bay microfacies,fan delta front underwater distributary channel,tributary bay sedimentary microfacies,shore-shallow lake shore-shallow lake mud,sand bar sedimentary microfacies,and semi-deep lake mud sedimentary microfacies.Fan delta sedimentary facies,the sediments are mainly coarse clastic,poorly rounded and sorted,mainly angular and sub-angular,with typical characteristics of mixed accumulation.The fan delta plain is the transition between the onshore part of the fan delta and the alluvial fan.The study area is mainly distributed on the side of the sedimentary fault of the faulted lake basin.Among them,the distributary channel deposits are more developed in the fan delta plain of the study area.Its lithology is mainly gray pebbly siltstone,purple gray pebbly siltstone,and gray silty mudstone.It is shown on the logging curve as toothed medium-high amplitude box shape and bell shape.The floodplain deposits are located in low-lying areas between distributary channels or between individual fans.The sediment grain is relatively fine as a whole,and the lithology is mainly composed of mudstone,silty mudstone and argillaceous siltstone,with thin layer of sandstone and sandy gravel deposits locally.The color of mudstone is generally gray and gray-green,and purplish red appears locally.On the conventional logging curve,the microfacies are mostly characterized by high GR value and low amplitude toothed line,and local mutation is characterized by low GR value,with finger-like logging response.The fan delta front deposit is the underwater part of the fan delta,which is the most active part of the fan delta deposit,and is composed of sandstone and dark mudstone.Its sediment lithology is mainly sandy conglomerate,pebbly sandstone,mixed with dark gray and grayish black mudstone,which are interbedded with each other in different thickness.The underwater distributary channel is the underwater extension of the onshore distributary channel,and its sedimentary characteristics are similar to the onshore distributary channel.The grain size of the sediment is obviously fine,mainly composed of gray glutenite,siltstone and argillaceous siltstone.The overall performance is the positive rhythm overlay layer with thick bottom and fine top.On conventional logging curves,it is shown as toothed medium-high amplitude box type and bell type.The tributary bay is located on both sides of the underwater distributary Yellow River channel,mainly composed of gray,dark gray,gray-black mudstone and silty mudstone,with thin gray siltstone.On the conventional logging curve,the sedimentary microfacies are generally low amplitude toothed linear.The sedimentary environment of the lake area is complex,and it mainly receives coarse clastic sediments from the lake shore.Its sediment lithology is mainly composed of black and gray-black mudstone with thin sandstone.Due to the complex hydrodynamic conditions and the strong scouring and screening effect of lake waves,the sedimentary structures are also complex and diverse.The microfacies of the sand bar are mostly pure fine sandstone and siltstone,and the conventional logging curve shows a low-amplitude finger-like.The shore-shallow lake mud microfacies are mainly composed of large sets of black,gray-black mudstone,silty mudstone,and black carbonaceous mudstone with thin layers of siltstone.The logging curve shows a low-amplitude toothed line.Semi-deep lake deposits with a small range of development are mainly thick black mudstone deposits,and the logging curve shows a low-amplitude toothed line.The SQ1 of Yingcheng Formation is the initial rifting period,and the lake basin begins to develop.The distance between the provenance area and the sedimentary area around the basin is short,and the elevation difference is small.The fan delta sedimentary system is developed on the east and west sides of the depression,and then enters the lacustrine transgression and highstand system tract.At the same time,the steep slope area becomes steeper under the influence of the lower volcanic rocks,and the lakeside facies begins to appear in the north of the depression;The water level of SQ2 Lake rises to the maximum flooding level and then begins to decline,and the fan delta extends to the center of the lake basin.The water surface of SQ3 drops,the water body becomes shallow,and many fan deltas are developed at the edge of the lake basin.Coastal lake and semi-deep lake facies are developed in the center of Deshen 111 well site.Several small fan deltas are developed in SQ4 with Deshen 83 well as the center,and the scale of the fan delta is reduced due to the restriction of material supply.SQ5water body changes from shallow to deep,and large-scale fan delta is developed around the depression with sufficient material supply.SQ6water body changes from deep to shallow.Under the condition of sufficient material supply,the scale of the fan delta becomes larger and extends to the center of the lake basin.The lacustrine facies expanded with the expansion of the basin during the SQ1-SQ6 period.The SQ1-SQ3 sedimentary period is characterized by continuous extension,the sedimentary center moves from north to east,and the sedimentary range is gradually expanded,which is a complete cycle of rising and falling of water body.During the sedimentary period of the first member of Yingying Formation,strong volcanic activity is often accompanied by the development of large area crater facies,near crater facies and intrusive rock facies.During the SQ4-SQ6 sedimentation period,the sedimentation center moved northward as a whole,developed multiple sedimentation centers,and also experienced the process of rising and falling of water body.4.The tight sandstone reservoirs of Yingcheng Formation in Baojia Sub-Depression of Dehui Depression depression are feldspar sandstone and lithic feldspar sandstone.The reservoir space types are intra-granular dissolution pore,intergranular pore and fracture.The reservoir physical property is low porosity-extra low porosity,extra low permeability reservoir.Reservoir properties are mainly controlled by sedimentary environment,diagenesis and mineral composition.The distribution of clastic particles in the study area is uneven,ranging from silty sand to gravel grade,with an average grain size interval of 0.032～4.0 mm,and some gravel reaching more than 20 mm.The particle separation is medium to poor,rounded and sub-angular,with high impurity content and low structural maturity,reflecting the characteristics of rapid deposition near the source.The average content of quartz,feldspar and rock debris is 37.9%,42.6%and 19.5%respectively,which are feldspathic sandstone and lithic arkose.The reservoir space type of the reservoir is composed of intragranular corrosion pores,intergranular pores and fractures.Intragranular dissolution pores account for 89%of the total pores,and feldspar dissolution pores are the most developed.The reservoir porosity in the study area is between 6%and 12%,with an average of 7.40%,and the reservoir permeability is 0.002×10-3～1.0×10^-3μm²,average permeability 0.070×10^-3μm²。The physical properties of the reservoir are poor,and it is comprehensively evaluated as low porosity-ultra-low porosity and ultra-low permeability reservoir.The pore throat distribution ranged from 0.001 to 0.5μm,the average pore throat radius ranged from 0.010 to 0.166μm,the roar distribution ranged from 0.5 to 1.0μm,the average throat length ranged from 12.236to 14.488μm,and the average was 13.178μm.Pore roar,accounting for a large volume of the total pore volume,poor connectivity,mostly in independent closure or narrow roar,little contribution to the permeability of the reservoir;Macropore roar,however,accounts for a smaller total pore volume and has better connectivity.Reservoir properties are mainly controlled by sedimentary environment,diagenesis and mineral composition.Fan delta front reservoir has the best physical property.Diagenetic compaction and cementation destroy the pore structure of the reservoir and reduce the porosity and permeability of the reservoir.The dissolution of feldspar and cuttings forms a new reservoir space and improves the reservoir physical property,while chlorite and illite increase the porosity and curvature of the bellow,reducing the pore space and permeability of the reservoir rock.5.It is clear that volcanic activity is the main controlling factor for the enrichment of tight gas reservoirs.It promotes the hydrocarbon generation and expulsion of hydrocarbon source rocks,provides a good reservoir space for the enrichment of gas reservoirs,promotes the formation of traps,and provides a guarantee for the formation and enrichment of tight sandstone gas reservoirs.The temporal and spatial configuration of volcanic activity and hydrocarbon generation and expulsion periods ensured the accumulation and enrichment of tight sandstone gas.The volcanic activity improved the formation temperature and pressure system and accelerated the hydrocarbon expulsion process.Volcanic activities not only did not destroy the gas reservoir,but also had a good time and space allocation with regional hydrocarbon generation and expulsion stages,ensuring the formation and enrichment of tight sandstone gas reservoirs.The volcanic activities affect the sedimentary filling of the lake basin,control the distribution of reservoirs,promote the development of high-quality reservoirs,and provide a good reservoir space for gas accumulation.Affected by volcanic activity,the strata are distributed between the volcanic activity area and the controlled depression fault.The denuded volcanic rocks provide a certain source of material for the sediments.Medium and acidic extrusive rock fragments are generally seen in the sandstone.Later dissolution forms the reservoir space（accounting for 20%of the total reservoir space）,and the tuffaceous components are also dissolved to form tuffaceous dissolved pores（accounting for15%of the total reservoir space）.At the same time,the late volcanic activity in the study area led to the intrusion of intrusive rock into the consolidated rock stratum,causing the arch fracture of the surrounding rock,and the development of fractures（accounting for 3%of the total reservoir space）.Volcanic activity improves the quality of reservoir.The early and middle stages of volcanic activity have"wrapped"the whole Yingcheng Formation,promoted the formation of traps,and are important factors for gas accumulation.The early volcanic activity developed a large volcanic group,which controls the sedimentary boundary of the Yingcheng Formation depression.Under the influence of the late tectonic activity,the lateral shield in the updip direction was formed.The tuff developed in the middle volcanic activity is covered by the dense sandstone reservoir in the first member of Yingcheng Formation.The tuff stratum is widely distributed and relatively stable in thickness,covering the entire sandstone reservoir.The early and middle volcanic activities provided favorable trap conditions for gas accumulation.