The improvement of modelling in carbonate reservoir by dual porosity via geological and engineering approach

Abstract

Carbonate heterogeneity has complex post-depositional diagenesis, superimposed on the original microstructures inherited from the initial deposition environment during sedimentation. This causes massive complexity in pore shape, pore size, pore connectivity, and distribution of pores in carbonate, which leads to the complexity in carbonate reservoir modelling domestically. The porosities of carbonate rocks can be separated into three types: macro-porosity (connected porosity), mesoporosity (unconnected vugs and pores result from diagenesis dissolution) and micro-porosity (isolated porosity). This thesis focuses to propose an improved dual porosity carbonate modelling approach. The main contribution of this work is to determine the method to recognize and quantify dual porosity in carbonate through six (6) information that can be obtained from a reservoir, namely geological core description and photomicrographs, RCA and SCAL analysis, nuclear magnetic resonance NMR, mercury-injection capillary pressure MICP, pressure transient analysis and a bonus for brownfield, production pressure profile. To test the effectiveness to quantify dual porosity, Field B in Central Luconia, Sarawak is selected as a study candidate. Data from conventional core provide direct observation of the rock pore geometry via photomicrograph, a diagenetic process which leads to segregation of macro and micro-porosity. Other petrophysical properties obtained via routine core analysis (RCA) and special core analysis (SCAL) provide the reservoir poro-perm condition. The mercury injection capillary pressure (MICP) curves translate the reservoir pore throat efficiency into macro and micro-porosity. Nuclear magnetic resonance (NMR) T2 relaxation distribution yields a bimodal trend for the dual-porosity reservoir. The pressure derivative transient analysis graph exhibits a Vshape yielding a dual-porosity reservoir. The pressure surveillance plot in the brownfield shows a flattening pressure depletion trend indicating microporosity charging to the production. These results are incorporated into a multiscale model and the simulation matches the reservoir's historical data and the type of dual porosity is identified as a matrix (connected) – matrix (isolated) type. Identifying the dual porosity in the carbonate reservoir enables the management to understand the reservoir hydrocarbon production and subsequently, lay out a proper reservoir management plan.