Experimental and Simulation Study of Water Shutoff in Fractured Systems Using Microgels

Abstract Conformance control has long been a compelling subject in improving waterflood oil recovery. By blocking the areas previously swept by water, subsequently injected water is allowed to access the remaining unswept portions of the reservoir and thereby increase the ultimate oil recovery. One technique that has recently received a great deal of attention in achieving the so-called "in-depth water shut-off' is preformed gel injection. However, processing and predicting the performance of these gels in complex petroleum reservoirs is extremely challenging. As target reservoirs for gel treatments are mainly those with fractures or ultra-high permeability streaks, the ability to model the propagation of gels through a fractured reservoir was considered as a new challenge for this research study. The primary objectives of this work are to conduct laboratory work to understand the transport and propagation of microgel through fractures and develop conformance control schemes using a reservoir simulator to help in screening oil reservoir targets for effective particle gel applications to improve sweep efficiency and reduce the water production. Fractured experiments using transparent apparatus were performed to observe gel transport in matrix and fractures. The same set up was used to observe the effects of gel strength, gel particle size, and fracture size on gel transport. Numerical simulation of fluid-flow in fractured reservoirs can be computationally difficult and time consuming due to the large contrast between matrix and fracture permeabilities and the extremely small fracture apertures and the need for using unstructured gridding. In this work, a model that accurately represents the complex reservoir features, chemical properties, and displacement mechanisms is developed. The five-spot transparent fracture experiments allowed us to identify the transport mechanisms of microgels through fractures-conduits and also the control variables. With an integration of comprehensive gel transport modules and a novel Embedded Discrete Fracture Modeling (EDFM), gel rheological and transport properties of shear thinning viscosity, adsorption, resistance factors, and residual resistance factor, using multiple sets of fractures with dip angles and orientations were captured. The models were validated against lab measurements and implemented into a reservoir simulator called UTGEL. The mechanistic models and numerical tool developed will help to select future conformance control candidates for a given field and to optimize the gel chemistry and treatment.