Distribution Characteristics of the Mudstone Interlayer and Their Effects on Water Invasion in Kela 2 Gas Field

Abstract

The reservoirs of Kela 2 gas field are mainly thick-very thick-bedded sandstone inter-bedded with mudstone. In the past 15 years of high-speed development, Kela 2 gas field has been facing the challenge of inhomogeneous water invasion. In order to understand the water invasion laws, based on seismic, logging, core, and production dynamic data, the characteristics of the non- pay interlayers and their sealing ability are analyzed. Then the effects of interlayer, faults, fractures as well as the high permeability formations on the migration of edge and bottom water were discussed. The research results show that: (1) Mudstone interlayers can be divided into two types, one is continuously distributed in the whole area with a thickness of about 10−50 m, the other is discontinuously distributed in the field with an individual thickness generally less than 2 m. (2) The interlayer sealing ability is closely related to the thickness of interlayer and fault throw. The interlayer at top of the Baxigai Formation, together with the interlayers at bottom of the Bashijiqike Formation has a stronger sealing ability than the others. (3) Controlled by the geological characteristics of the gas field, water invasion laws are varied in the different regions. In the west and east regions, Edge water can induce the seriously inhomogeneous water invasion through the relatively high permeability layer; while in the south-central region, the bottom water invasion is relatively moderate because the thick-bedded interlayer weakens the energy of water from deeper bed; in addition, in the SW region, bottom water breakthroughs along faults vertically and then invades along the natural fractures and the relatively high permeability layer, which led to water flooding of gas wells in the area. This study is of great significance to water control and stable production of the gas field.