Completion fluids contain chemicals such as surfactant, friction reducer, clay stabilizer, scale inhibitor and biocides that are pumped downhole during hydraulic fracturing operation to enable oil recovery from shale reservoirs. These chemicals carry a significant cost themselves that needs to be optimized for an economic completion job. Additionally, the choice of chemicals can either have a positive effect on production or can cause degradation to the oil flow capacity.
Incompatibility of completion chemicals with reservoir fluids, formation brine and/or oil, can lead to problems such as precipitation, phase trapping, viscous emulsion generation in the proppant pack. A thorough screening of each chemical is essential to discern any negative impact that it can have on the proppant and the rock matrix formation. Pumping undesirable/incompatible chemicals having a high Interfacial Tension (IFT) with crude will result in poor flow characteristics that can have a detrimental effect on oil production rates and consequently on project economics.
Several tests have been designed and implemented in this paper with the aim to select completion fluids that improve oil recovery from the rock and promote its flow in the proppant pack while also minimizing permeability degradation in the shale matrix. Screening tests (Phase I tests) developed here can identify incompatible chemicals so they can be eliminated or replaced with those exhibiting a better compatibility with crude oil. In addition, sensitivities studies are performed by varying chemical concentrations of chemicals such as surfactants, clay stabilizers, etc. so that the completion fluid recipe could be made more cost effective.
Hydraulic fracturing operations involve the injection of frac water (fresh, produced, or a mix) and sand at high pressures downhole to fracture the rock for oil and gas production. In a typical operation various chemicals are mixed with frac water to make a completion fluid recipe; the aim of the chemicals is to prevent reservoir damage and enhance oil production to achieve maximum Return on Investment (ROI). There could be several mechanisms through which completion chemicals can interact with formation fluids and rock. Understanding these interactions is important to design and optimize completion fluid recipe.