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Study On Reservoir Characteristics And Favorable Reservoir Evaluation Of Daxing Conglomerate In Langgu Depression

Posted on:2012-02-22Degree:MasterType:Thesis
Country:ChinaCandidate:H W ZhouFull Text:PDF
GTID:2120330332489130Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
Daxing conglomerate lies on the steep slope zone of Langgu depression and it is characterized by a series of superposed nearshore subaqueous fans which can be further divided into three conglomerate groups including Caiyu conglomerate group, Jiuzhou conglomerate group and Gu'an conglomerate group from SW to NE. The success of Xing 9 well area indicates that Daxing conglomerate has much higher exploration potential. Combining the data of cores, petrographic thin sections, scanning electron microscope (SEM) photos and X-ray diffraction analysis, in this paper we have studied the petrologic characteristics of reservoir, diagenesis types, reservoir space types and their genetic mechanism in details. Our research emphasizes the main controlling factors of reservoir development and builds a set of reservoir evaluation method finally which helps us conduct reservoir classification evaluation and forecasting.Daxing conglomerate is mainly composed of carbonate gravels which include limestone and dolomite. The rock structure can be subdivided into three types including grain-support, carbonate matrix-support and muddy matrix-support according to supporting type and matrix composition. The study shows that petrologic characteristics of reservoir are markedly divisional and it is the existence of grain-supported rocks which are mainly composed of dolomite gravels that makes Jiuzhou conglomerate group superior to other districts.This paper has established the diagenetic sequence and stage of Daxing conglomerate, and finds the main reservoirs (the middle and lower parts of the third member of Shahejie Formation) are in"A"and"B"periods of middle diagenesis. In middle diagenesis, dissolution effect of acidic fluids controls the first two secondary porosity belts in the longitudinal profile, while the third porosity belt in deep layers is affected by the inheriting effect and preservation of abnormal high pressure in late diagenetic period.The reservoir space types in our study area include intragravel pore, intergravel pore and fissure which are formed by the genetic mechanism of secondary dissolution effect, inheriting effect, structural effect and pressure dissolution effect. It is indicated that siliceous dolomite from Jixian System in source area can be carried down to Langgu depression in the form of boulders which make all the solution pores and caves formed by weathering and leaching effects in surface environment preserved by quick deposition and abnormal high pressure. We call the pores which originate from mother rocks and then are preserved in gravels inheriting pores, and they are unique in Daxing conglomerate.Based on the analysis of reservoir controlling factors, we build a set of reservoir evaluation method finally which takes genesis, facies, composition, structure and burial depth as evaluating indicators. Combining the analysis of single well facies, correlation of cross sections, plane distribution of sedimentary facies, petrologic characteristics and diagenesis types, we should evaluate the reservoir and optimize seismic prediction targets following the steps of genetic classification, facies identification, characteristic analysis (composition and structure) and depth calibration. Overall, the grain-supported conglomerates located in porosity belts which are mainly composed of dolomite in braided river channel of grain flow nearshore subaqueous fan and subchannel of gravity flow channel are the most favorable reservoir belts.
Keywords/Search Tags:Langgu depression, Daxing conglomerate, Reservior, Diagenesis, Evaluation
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