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The Geophysical Response Of Non-sandstone Reservoirs In Salt Beds In Chen Tuokou District

Posted on:2016-04-11Degree:MasterType:Thesis
Country:ChinaCandidate:D ZhaoFull Text:PDF
GTID:2180330464461964Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
When it comes to the non-sandstone reservoirs in salt, it means low porosity and permeability reservoir under the background of lake sedimentary, which mainly influenced by the factors of ancient water depth, climate, material supply and chemicals. Its lithology changes frequently, mostly characterized by millimeter interbedded mudstone, shale, argillaceous dolostone, and gypseous mudstone. As a peripheral recess of Jianghan Basin, it is very important to deepen understanding and increase production, which although can not be compared with the other three major depression in resources amount. Applied the theory of petroleum geology, mineral petrology, organic geochemistry and geophysics, the paper analyze the non-sandstone reservoirs in salt in the Lower Member of Paleogene Xingouzui Formation in Chen tuokou Depression. The main achievements are as follows:1. Studied on the provenance direction.We analyzed the statistical data of heavy mineral and lithology from adjacent Laoxin-Xingou and Chen Tuokou Depression, finding that the maturity of heavy mineral was from low to high, the sandstone percentage gradually decrease while the mudstone percentage and the maturity of mineral composition increasd gradually. Moreover, the rock grain median diminished and the sorting turn good, which means the structure maturity of clastic rocks get better. All these suggested that the debris source of sandstone in northern Chen Tuokou Depression was the Laoxin-Xingou branch of Hanshui provenance.2. Carried out the study of sedimentary facies and plane distribution rules.(1) The main lithology of this area is mudstone (including shale, gypsum mudstone, dolomitic mudstone, etc.), dolostone (including dolostone, shale dolostone, etc.) and little siltstone in II oil group. There may be a small amount of residual oil in the shale, which mainly act as the source rock, but reserved by dolostone and siltstone. We identify 5 types of lithofacies. They are dark mudstone facies, mudstone-calcium facies, shale facies, argillaceous siltstone facies, argillaceous dolomite facies and so on;(2) We divided the sedimentary facies systems combining with facies markers, such as core data (mudstone color, size, fossils), logging data (electrofacies) and seismic facies. Based on the analysis of single well sedimentary micro-facies, the plane distribution characteristics of sedimentary facies were made out by combining the research of seismic attribute abnormal area and contrast analysis of well-tie sedimentary facies. The shallow-water delta sedimentation of the III oil group could be subdivided into two sub-facies, including delta front which developed 4 kinds of micro-facies such as well-developed subaqueous distributary channel, inter-distributary bay, mouth bar and front sheet sand, while pro-delta that contained two micro-facies like front delta mud and slump sand body. The interval II oil group was shore-shallow lake sedimentation where the lake is flat terrain, the weak wave action can’t spread to the shore, and the material supplying dominates by clay. It can be subdivided into dolomite flat, mudflat, mixed flat, gypsum-mudstone flat etc. The mudflat and mixed flat developed well.3. Combined the geophysical methods to analyze the Log response to the non-sandstone reservoirs in salt.(1) From log analysis, we conclded that density (DEN) and acoustic time (AC) become larger with increasing depth, while gamma ray (GR) and Compensated Neutron (CNL) tend to be smaller. Summarized as:GR and Z can better distinguish lithologic association with a monotonically decrease, while DEN has stacked in dolomite and mudstone, which is difficult to distinguish, CNL has the worst effect;(2) Compared parameters’characteristic in different reservoirs, the crossplot study of different parameters show that RT of the oil/water reservoirs is 2.8-6.5Ω·m, pure oil (heavy oil-bearing shale) reservoirs is high to 49.4Ω· m, AC is 198-236 us/m, reflecting the compactive reservoir; AC and DEN can better distinguish fluid;(3) According to the study of lithology, sedimentary combination characteristics can feature log response, we analysis as following:bell-shaped or box-shaped of underwater distributary channel microfacies; micro teeth or finger-shaped of bay tributaries; Funnel-shaped of estuary dam; fingers, funnel-shaped of Sheet sand; tooth’s bell of the former Delta, with abnormal low amplitude curve; Finger beach sand; tooth shape of mud; bell-shaped with micro-toothed cloud dolostone flat based on GR, SP, RT and AC curves.4. Combine the geophysical methods to analyze the Seismic response to the non-sandstone reservoirs in salt.(1) From variable thickness model of Ⅱ oil Group in Chen 102 well, we can draw:as the thickness change, when the angle is zero, the incidence reflection amplitude is positive, the larger of angle, the smaller of reflection amplitude, which is significantly positive. In the AVO attribute crossplots, AVO abnormal response mainly located in Ⅰ, Ⅱ and Ⅲ quadrant. With the increase of thickness, it comes from Ⅲ quadrant to Ⅱ quadrant. The value of P and G first increases from negative, then decreases. G value maxima appear in the 60m; From the original model, it can be drawn out:in oil layer, the P and G values are positive, located in quadrant Ⅱ, the amplitude increases with increasing angle; in aqueous layer, the P is positive, G is negative, amplitude decreases with increasing angle;(2) According to the seismic stratigraphic principles, we combined with external morphology, internal reflection structure and seismic properties of seismic reflection lineup. It can be divided into four kinds of typical seismic facies:parallel sheet facies, sub parallel sheeted drape facies, wedge-shaped seismic facies, seismic facies filling shaped, which mostly reflect the lower shallow water delta-lacustrine sedimentary in this area;(3) Despite the two-dimensional seismic data is in poor quality, we conclude that RMS amplitude and mean instantaneous frequency can be identified to study lithology through the analysis of seismic attributes:mudstone is the lowest of RMS amplitude values, generally 0.2-0.4; while sand is 0.6-1.7; as the high impedance cream rock, its value is generally 3-4 from the seismic sedimentary characteristics and provenance analysis law.
Keywords/Search Tags:Chen Tuokon Depression, Non-sandstone reservoirs in salt layers, Log response, AVO forward modeling, Seismic response
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