The Characterization Of Ultra-low Permeability Sandstone Reservoir And Development Technology In Anpeng Oilfield

There developed tight formations and low-porosity and low-permeability reservoirs inAnpeng Oilfield, Biyang Depression, southwestern of Henan Province, China. This paperdescribed the features of ultra-lowpermeability reservoir and development technologies ofultra-lowpermeability reservoir. The buried depth of reservoir is 2800-3100m. The reservoirs arecomposed of fan-delta sedimentary system. The micro-facies can be subdivided into six types.The composition and texture maturity of reservoir rocks is lower. The principle type of reservoiris sand and sand-conglomerate. The reservoir porosity distribution range 5-6%, the permeabilitydistribution range 1-2×10-3μm2, the mean radius distribution range of reservoir is 0.47-1.06μm.Rapid accumulation, sophistication of different grain sizes, low maturation of texture andcomponent are the key factors that cause low permeability.The paper described the reservoir fracture characteristics. The natural fractures were welldeveloped in the reservoir. Adopt advanced technique such as oriented coring to get the fracturesorientation. The rosette azimuth diagram indicated the fractures orientation range from E90toSE110. Lots of fractures are in the form of high degree or vertical type. The general spacebetween fractures is 2-3 cm. It belongs to the extension and shear fractures. The regional tensilestress is the causes of fracture. The fracture identification technologies such as the oriented coretechnique and acoustic-electric imaging log were used to get the occurrence and distribution offractures. The fractures length distribution range 4-30cm, the fracture apertures are smaller than1000μm, the fracture density is 0.7 per meter, the formation fracture porosity range 0.2-0.3%.The reservoir fracture development periods are analyzed in Anpeng Oilfield, BiyangDepression. There are some secondary calcite fillings in the fractures. The determine ofsecondary calcite stable isotope which fillings in fracture and the acoustic emission tests of thereservoir rocks indicate that there are four fracture generations. The second generation is themain fracture period. There are two main factors to affect the fracture developing, one is thestructure stress field, another is the nature and the thickness of the reservoirs. For fractureprediction we establish the relationship between thickness and fracture space.The analysis on reservoir depositional system indicates the genesis mechanism of Anpengstructural nose and its connection with the generation of reservoir fractures. Point out theco-effect of differential compaction and differential depression are the genesis of Anpengstructural nose. Give the distribution of major principle stress and major principle curvature ofoil measure. Point out the synthesis evaluation of fractures distribution of oil measure in AnpengOilfield .The liquids properties of reservoirs in Anpeng Oilfield are complicated. There are black-oilreservoir,volatileoilandcondensategasreservoir.Thereservoirfeaturesareultra-lowpermeability and low natural well production. Through reservoir evaluation, the papersuggests three methods to acquire cut-off value of ultra -low permeability clastic reservoirswhich bearing various fluids. Those are Hobson method, production ability method andbuoyancy method. In the end, this paper proposed the cut-off value for the effective developmentof extremely -low permeability oil and gas field.Finally, aimed at the reservoir feature of ultra-lowpermeability and low natural wellrate(1.5t per day), basis on reservoir fracture identification and distribution study, the formationstress field analysis indicate the direction of artificial fractures are accord to the direction ofmajor principle stress. In order to enhance the oil recovery of water-flooding, through reservoirfracture identification and distribution study, the paper suggests corresponding developmenttechnologies, optimal flooding patterns in fractured low-permeability sandstone reservoir.Because of the generally low pressure transfer-rate, the producer-injector spacing should berelatively close. Flooding pattern is with the well array direction at 45b with the fracture Strike.An optimized flooding pattern in fractured low-permeability reservoir should delay directionalwater break-through, prolong water flooded time. This paper suggests to adopt stimulationtreatment such as hydraulic fracturing, high pressure injection etc. to improve production rate.Through the hydraulic fracturing, the well production increase from 1.5t to 14.2t per day, thosemeasures are ensured for the development of ultra-lowpermeability oilfield effectively andenhancement the economic benefit.