New Insight to Wormhole Formation in Polymer Gel During Water Chasefloods Using Positron Emission Tomography PET

Abstract

Abstract Polymer gel is frequently used for conformance control in fractured reservoirs, where it is injected to reside in fractures or high-permeability streaks to reduce conductivity. With successful polymer gel conformance control in place, increased pressure gradients across matrix blocks may be achieved during chasefloods, diverting water, gas or EOR chemicals into the matrix to displace oil. Knowledge of gel behavior during placement and chase floods is important, because it largely controls the success of subsequent injections. Polymer gel behavior is often studied in core floods, where differential pressure and effluents from fracture and matrix outlets give information about gel deposition during placement and flow paths during chasefloods. The work presented in this paper utilize complimentary PET-CT imaging to quantify the behavior and blocking capacity of Cr(III)-Acetate HPAM gel during chase waterflooding. In-situ imaging provides information about changes that may not be extracted from pressure measurements and material balance only, such as changes in local fluid saturations and dynamic spatial flow within the fracture and within the structure of the gel network. Polymer gel was placed in core plugs with longitudinal fractures that connected the inlet and outelt, and chase water was subsequently injected to measure the gel blocking capacity. The water phase was labelled with a positron emitting radiopharmaceutical (F-18) to visualize and quantify local flows with positron emission tomography (PET) during gel rupture and subsequent flooding. Using PET, we study gel rupture and the development of wormholes during gel erosion after rupture as a function of flow rate. A particular strength with access to dynamic, local flow patterns is the direct comparison to global measurements, such as differential pressure and production rate, to verify existing gel behavior models.