The Analysis Of Exploration Prospects Of Chang63in Ansai Oilfield

Ansai Oilfield located in the center of Ordos Basin, loess plateau in northern Shanxi, with the structure in the middle of Yishan slope belt, is the earliest developed onshore oilfield with extra low permeability. This paper made systematical study on the Chang63of Triassic Yanchang Formation, the primary oil-bearing measure.The present paper summarizes the hydrocarbon enrichment roles and finds out the favorable hydrocarbon accumulation, but also sorts favorable areas and optimize block of production by using the sedimentary petrology, reservoir geology, logging geology and petroleum geology as the thesis thoughts and guiding philosophy; collecting field profile photos based on the previous research achievements; observing and describing cores and sampling,combined with logging curve and interpreting production logging data, porosity and permeability of sandstones as the main methods, by means of sedimentation analysis, reservoir assessment, entrapment forecasting and analysis, reservoir dissected in development block.Firstly, based on the stratification standard of Changqing Oilfield, Zhangjiatan shale and key beds K2、K3, we divided Chang63into three sand group of Chang631,Chang632and Chang633and drew its top construction. And combined with deposit system and single factor analysis, it is concluded that there developed two provenance systems located at the northern-west and southern-east part of Ansai by analyzing the distribution of depositional systems from layer. The northern provenance system in northern-west stretching from northern-west to southern-east and the northern-east provenance system developed in southern-east from northern-east to southern-west, they all belongs to delta front subfacies. Then analyze the reservoir lithology, physical characteristics, pore types, pore assembly types and make a comprehensive evaluation. The Chang63reservoir rock is mainly arkose. The reservoir pore space mainly consists of intergranular pores, from low porosity and low permeability to particular low generally. By comparing physical properties, referring to the reservoir evaluation criterion, we can project that Chang63’is the best, then Chang632.Chang63in Ansai Oilfield as monoclinal stratum, the structural traps are not well developed. The cause type is mainly sandstone up pinchout trap. In different provenance system, traps’development characteristics in different sand belt are not same. The southeast branch of the northern provenance system develops lithologic traps while northern-east provenance system doesn’t. According to the overlapping of the structure and sandstone distribution map, combined with the logging interpretation results and testing, analysis the lithologic traps, found eighteen lithologic traps, including five real traps and twelve evaluation traps. From the analysis of hydrocarbon distribution, it is mainly controlled by sedimentary system, namely the north provenance system, but north-east material provenance system has no reservoirs exist generally, only in the case of lithologic trap developing locally, it existed small scale reservoir. After comprehensive research result, combined with present-founded achievement about hydrocarbon distribution and sedimentary system, it was considered that hydrocarbon distribution was controlled by sedimentary system in the northern part of the Ordos Basin, in short, Sedimentary System Control Reservoir Theory. Most hydrocarbon accumulation zone of Ansai Area are all controlled by north provenance system, mainly distributed in the northwest, however, the probability of pool forming is poor in the reservoir when under the southeast and northeast provenance system.Finally, on the basis of sedimentary,reservoir, trap analysis and evaluation reservoir-forming regularity, analyze the real traps and evaluation traps and set up an optimization model for favorable production area. Chang631developed eight favorable areas including four real favorable areas while Chang632developed three favorable areas including two evaluation favorable areas and one prospective favor. Overlap favors in different layers and identify the favorable production area based on optimization area, we discovered these three regions are optimal distribution area.