The Seismic Facies Analysis Of ShaⅡ-Dongying Reservoir In Wen’an Slope Of Baxian Sag

The research on sedimentary facies plays an extremely important role in oil, coal and other mineral resources exploitation. Some necessary methods are required for study and exploration, because strata are deeply buried underground.By comparing with study on the sedimentary facies in outcrop area, core data is the only method used to observe and analyze the sign of sedimentary facies which is able to reflect the information of sedimentary environment. It’s getting hard to study sedimentary facies due to the discontinuity and low exploration rate of exploratory well coring. The logging analysis, based on logging data, can get sequential interpretation of sedimentary facies, but the explanation of results have great multiplicity. And even if the logging analysis is sufficient, the interpretation is correct, it’s still a narrow view in explanation of sedimentary facies. Therefore, we have to dig more wells to get the plane distribution of sedimentary facies,, However, it’s obviously uneconomical. In addition to the two methods mentioned above, a new method, based on a few well, is required to have a good mastery in plane distribution characteristics of sedimentary facies in order to ensure the correctness of the sedimentary facies explanations.In order to meet these urgent demands, the seismic facies analysis method is invented. Seismic facies are the seismic response of sedimentary facies and geological body which are constrained by kinds of seismic facies parameters. On the base of seismic facies, seismic facies analysis can be made to get inferences on sedimentary facies in plane. Seismic exploration data is essential in oilfield exploration which can be acquired from the early period of exploration and contains extremely rich geological information. Seismic facies analysis is an important method in making sedimentary facies study in an area with sparse well. It can help to conjecture on geological conditions for the area with no drilling wells on the basis of spreading the geologic feature of existing wells in the plane. Under the help of the close connection of core data, logging data and seismic data, we are able to make accurate analysis of sedimentary facies in both horizontal and vertical so that the distribution of reservoir can be predicted.From the reservoir distribution characteristics in Wen’an slope of Baxian sag, the main target layers of the work area are Guantao Formation, Dongying formation and Shahejie Formation. In the work area, the reservoirs are well-developed and have good physical properties, but the sandstone reservoirs are not found interbedded with mudstone, which will develop several sets of reservoir-seal assemblage. The Dongying formation and Shahejie Formation are dominated by river and floodplains deposits which create the characteristic of great changes in both vertical and horizontal and poor continuity of reservoirs in this area. Therefore, the key question in reservoir study is how to effectively identify and predict the reservoir in this area.This article uses the seismic facies analysis technology to make a qualitative research on fluvial strata in Wen’an slope on the basis of sequence stratigraphic research. The specific method applied is the traditional" metoposcopy ".According to the seismic facies indicators, we can find kinds of progradational reflection configuration on the seismic profile to explain the main provenance location and the flow direction. After that, the phase region can be divided based on the difference of seismic reflection wave in amplitude, frequency and continuity. Follow the steps above, we can transfer the interpretative results on the seismic profile to the plane, and finally, the seismic facies evolution analysis can be discovered according to the seismic facies plane distribution map.After processing the study explained in this paper the following conclusion can be drawn:(1)Es2sequence shows "S"type foreset and weak amplitude reflection on the seismic profile.Comprehensive analyzing the sand body form of each facies, the flow energy and so on, we can conclude that the seismic facies of this sequence have characteristic of braided river-delta.(2)Eslx sequence retains similar sedimentary environment as Es2,it shows spare, discontinuousand medium-weak amplitude reflection on the seismic profile. In this area, the sequence shows the characteristic of shore lacustrine facies, and sand dam facies are well-developed in the south of work area.(3)Esls sequence shows short-tilting axis foreset and medium amplitude reflection on the seismic profile and locally contains similar imbricate and medium amplitude reflection. This sequence has the characteristic of braided fluvial facies.(4)Ed3sequence shows short-tilting axis foreset and medium-weak amplitude reflection on the seismic profile. It displays channel filling and the characteristic of meandering river fluvial facies.In a word, according to the comprehensive analysis mainly in seismic data and so on, the work area shows the whole developmental process from braided fluvial river delta facies to river meandering river in evolution of the sequence from Es2to Ed3.The features of seismic facies are obviously displayed in each sequence.