Diagenetic Facies Characterization for Deep Structures Under the Condition of Sparse Wells

Abstract

Generally, the favorable diagenetic facies belt of the reservoirs is the dessert for hydrocarbon exploration. Traditionally, the research of diagenetic facies is based on core analysis, as a result, it is difficult to make prediction under the condition of sparse wells and less cores. In order to solve this difficulty, the new method to predict the diagenetic facies should be researched. In this research, the low permeability sandstone reservoirs of East China Offshore Gas Fields are selected as the research area, and three research steps have been done. First, by using the core analysis, ACR (Apparent Compaction Ratio) and ADR (Apparent Dissolution Ratio) are selected as the discriminant parameters for the diagenesis, and the quantitative standards are established. Second, the rock-electric relationships according to the diagenetic facies are established, the relationship of well logging parameters (GR, DT, CNCF, RT, DEN) vs. ACR, and the same well logging parameters vs. ADR can be matched by using BP neural network method. Accordingly, the ACR and ADR of the whole well can be obtained, and the diagenetic facies in accordance with the ACR and ADR can be predicted. Third, the relationship of well-log and seismic data can be established. After that, the relationship of seismic attributes (Ip - p wave impedance, Is - s wave impedance, Vp/Vs - p and s wave velocity ratio) vs. ACR, and the same seismic attributes vs. ADR can be matched. After the three steps, the favorable diagenetic facies belt can be predicted by using seismic attributes under the condition of sparse wells and less cores. By using the above methods, the diagenetic facies in the research area can be divided into six types: mid dissolution and mid compaction; mid dissolution and mid-strong compaction; strong dissolution and strong compaction; mid-strong dissolution and strong compaction; shale-silty strong compaction; strong cementation. The previous three of the six types are selected as the favorable diagenetic facies. According to the quantitative standards of ACR & ADR, and the relationship of the seismic attributes vs. ACR & ADR, the diagenetic facies in the plane and vertical can be predicted by using seismic attributes. In the research area, three layers of Huagang formation have been selected by fitting the favorable diagenetic facies: Layer 1 (Shallow) corresponding to mid dissolution and mid compaction; Layer 2 (Mid) corresponding to mid dissolution and mid-strong compaction; Layer 3 (Deep) corresponding to strong dissolution and strong compaction. As a result, these three layers are considered to be the desserts for exploration and development. This paper presents a new quantitative characterizing system for diagenetic facies by combing core-logging-seismic. Furthermore, a new method to quantitative characterizing diagenetic facies by using seismic attributes is established for the first time. The innovative content presented in this paper can provide theoretical references for exploration of sandstone reservoirs under the condition of sparse wells, and also provide complement for the diagenetic facies characterizing theories.