A Laboratory Protocol to Investigate EOR by Surfactants During Pre-Loading of Parent Wells to Mitigate Fracture Hit

Abstract

AbstractGenerally, pressure and fluid communications between parent and child wells which is referred to as frac hit deteriorate the production performance of the parent well. Small pre-loading technique is one of the cost-efficient and operationally simple strategies to mitigate frac hit. However, the production outcome of the parent well is unsatisfactory after flowback of pre-loading fluid in most of the pilots. To overcome this negative impact, we intend to evaluate the extent of additional oil recovery by imbibition of fluids with two types of non-ionic surfactant additives (SF-1 and SF-2) during pre-loading and flowback processes. We utilize a high-pressure and high-temperature visualization cell to conduct the pre-loading experiments using Montney rock and fluid samples. We restore the initial reservoir condition in the core plug and then simulate the primary production stage of the reservoir to establish a depleted core plug. Then, we conduct two sets of experiments on the depleted core plug: 1) soaking the plug with SF-1 surfactant solution under atmospheric conditions and 2) pre-loading the depleted core plug with the SF-1 surfactant solution at a pressure of 3,500 psig and reservoir temperature of 78°C. We also pre-load an oil-saturated core plug with SF-2 surfactant solution at similar operational conditions. Our results show that 31.4% of the original oil-in-place is produced during the primary production stage with solution-gas drive as the dominant oil-recovery mechanism. We observe an additional 3.9% (of original oil-in-place) oil recovery due to counter-current imbibition of the SF-1 surfactant solution after soaking under atmospheric conditions. The interfacial tension reduction and wettability alteration are two possible oil-recovery mechanisms during surfactant soaking. Pre-loading the depleted core plug with SF-1 surfactant solution at a set pressure of 3,370 psig and a temperature of 78°C does not result in additional oil recovery. However, pre-loading the oil-saturated core plug with SF-2 surfactant solution at the same operational conditions results in an approximately 29.6% oil recovery. We observe oil droplets formed on the rock surface during soaking of the oil-saturated plug with SF-2 surfactant solution. We conclude that longer soaking periods may assist in additional oil recovery in core plugs with depleted state compared to the non-depleted plugs.