元坝礁滩相储层四性特征及其关系分析

Four Characteristics of Reef Shoal Reservoirs in Yuanba Area and Their Relationship

储层四性特征及其关系是气层、水层识别和储层评价的重要依据。通过岩心观察、岩屑录井及薄片鉴定,明确了元坝长兴组礁滩相储层岩性、物性、含气性及电性特征,采用常规测井、特殊测井及交汇图探讨了岩性、电性、物性、含气性之间的相互关系。元坝长兴组气藏为礁滩相储层,储层岩性以溶孔白云岩、生屑(含生屑)粉细晶白云岩、残余生屑(粒屑)白云岩、生物礁白云岩为主,孔隙度分布在0.53%~24.65%,平均为4.08%,属于孔隙型、裂缝—孔隙型储层,多以Ⅲ类储层为主,见少量Ⅰ、Ⅱ类储层;含气性差异大、总体为礁相储层含气性优于滩相储层、东部滩区优于西部滩区。通过四性关系研究表明物性受岩性控制明显,白云岩储层物性较好;储层含气时,电阻率为高电阻率背景下相对低值,含水时则为低值,含气性越好电阻率相对越高,但电阻率非常高时主要受岩性影响不再是含气性的反应。

For a reservoir, the four characteristics(including lithology, petrophysical property, gas property, and electric property)and their relationship are important for water and gas identification and reservoir evaluation. In this study, based on core observation,cutting mud logging, and thin-section identification, we analyzed the four characteristics of the reef shoal reservoirs of Changxing Formation, Yuanba area. Moreover, the relationship among these four characteristics was gained by means of conventional well logging, special well logging, and crossplot. Results show that(1) these reservoirs belong to reef shoal ones, which are composed of dolomite with dissolved pore, bioclastic powder-to fine-crystalline dolomite, residual bioclastic dolomite, bioreef dolomite;(2) with IIItype as the soul, they belong to porous, and fractured-porous reservoirs with porosity ranging from 0.53% to 24.65% and 4.08% on average;(3) there is big difference existing in gas property, totally it in reef reservoirs better than that in shoal reservoirs, and shoal area in eastern part better than that in western part;(3) lithology has an obvious effect on petrophysical property, and dolomite reservoirs have better petrophysical property;(4) while gas found in reservoirs, resistivity is relatively low value under high resistivity value whereas resistivity is low value when water found. In general, better gas property leads to higher resistivity. However, the highest resistivity is affected by lithology not reacts to gas property.