Optimization and Evaluation of a Novel Stabilizer Applied to the Strong Water-Sensitive Conglomerate Reservoir

Abstract

ABSTRACT Mahu Oilfield is the world's largest conglomerate oil field with 1.24 billion tons of petroleum reserves discovered so far. It is mainly a tight conglomerate reservoir with low porosity and low permeability. In the early stage of field development, it usually has characteristics of high flowback rate and low oil production rate. This may be attributed to strong water-rock interactions during hydraulic fracture operation. When water-sensitive minerals in rocks encounter water, clay expansion and particle migration occur, resulting in reduction of rock strength and fracture collapse. In order to choose a suitable anti-swelling agent for Mahu Oilfield, XRD, zeta potential, anti-swelling rate, immersion, Brazil splitting and other test means are used. Then, we evaluated the performances of inorganic salts and inorganic cationic polymers on clay swelling control and rock stability, and their combination and optimal ratio were also studied. The experimental results show that the clay content of the rock is up to 37.3%, of which 88% is the expandable montmorillonite mineral. The mixture of inorganic salt and inorganic cationic polymer can effectively inhibit the water-rock reaction by reducing the clay expansion and compressing the double electric layer on the rock surface. Through the test of swelling rate, it is found that the swelling rate of optimal reagent for montmorillonite can reach 92%, and the swelling rate of the reservoir rock powder can reach over 70%. The results of the rock immersion experiments show that the optimal stabilizer can ensure the strong water-sensitive conglomerate remains stable after soaking for 24h without dispersion. Compared with the KCl solution commonly used in oilfields, it can increase rock strength by more than 10% without increasing cost. The results of this study provide a solution for hydraulic fracturing in highly water-sensitive reservoirs. INTRODUCTION Mahu Oilfield is the world's largest conglomerate oil field with 1.24 billion tons of petroleum reserves discovered so far (Li et al., 2020). However, the reservoir is rich in water-sensitive minerals such as montmorillonite (Uddin, 2008). To effectively develop such tight reservoirs, hydraulic fracturing is commonly used (Li et al., 2015). Water injected during hydraulic fracturing interacts with reservoir rock, resulting in a decrease in fracture conductivity and well productivity (Ferguson et al., 2013).