Production Prediction Based on the Heterogeneity Analysis of the Tight Carbonate Reservoir in the Sichuan Basin, China

Abstract

Abstract Cambrian and Sinian tight carbonate reservoirs have become a breakthrough in natural gas exploration in China's Sichuan basin. The officially certified geological reserves proved that Moxi-Gaoshiti block is a giant gas field. However, carbonate rocks are diverse and their pore spaces are complex. The storage spaces in carbonate rocks can be divided into matrix pores, fractures, and dissolution pores. The strong heterogeneity in petrophysical properties brings lots of troubles in finding the sweet spot, and it is necessary to incorporate logging methods that provide insight into the pore geometry. This paper shows a method which incorporates Nuclear magnetic resonance (NMR), borehole images, and induced gamma spectroscopy. NMR is successfully utilized to characterize the pore geometry using a system built upon mercury injection capillary pressure (MICP) measurements and borehole image interpretation. The pores are divided into micropores, mesopores, and macropores. It shows a great advantage in production prediction because the macropores contribute to high initial production rates when they are well connected. The carbonate rocks are then classified into different types based on the pore geometry analysis of NMR and borehole image interpretation, which can be the guide for the further exploration. Case studies are presented from carbonate reservoirs in the Sichuan basin. A robust and comprehensive petrophysical description of lithology, porosity, pore geometry, permeability, rock types, and fluid saturations is presented. A new understanding of carbonate reservoir heterogeneity is established. The synthetic curve that incorporates several petrophysical properties turns out to be a good prediction of production. Our interpretation methodology was validated well with core data. This paper discusses a novel combination of open-hole logging tools for the heterogeneity analysis of tight carbonate reservoir in Sichuan basin, and it provides the geologists a handy technique to identify the best pay zone. The workflow can also be applied to other tight carbonate plays in China.