In-Depth Colloidal Dispersion Gels Improve Oil Recovery Efficiency

Abstract

SPE Members Abstract In the Rocky Mountain Region, a unique in-depth permeability modification process was applied to 29 field projects over the last 9 years. The process involves continuous, long term injection of environmentally sound colloidal dispersion gels. These gels provide a solution to in-depth channeling and crossflow problems inherent with waterflooding, which cannot be solved by near-wellbore gels. Use of colloidal dispersion gels in the field has never before been reported, yet the process has proven to have a phenomenal impact on efficiency of enhanced oil recovery projects. 22 of the projects were considered successful, resulting in improved oil recovery and reduced water production. Seven of the field projects were considered unsuccessful for a variety of reasons. Both successful and unsuccessful treatments are discussed, as both provide valuable insight into treatment design and application. Ultimate oil recoveries in successful treatments are in excess of 40 % OOIP, in highly heterogeneous matrix reservoirs with Dykstra-Parsons permeability variations on the order of 0.80. Chemical costs of $ 1.00 to $2. 00/BBL incremental oil recovered are typical, and this cost has decreased below $1.00 in more recent floods due to improved technology. The colloidal dispersion gel process was applied successfully at bottom hole temperatures up to 202 F. Oil viscosities are often high, from 10 cps to more than 20 cps at the reservoir bottom hole temperature. This paper provides a complete picture of project development from start to finish, including initial laboratory design, project selection criteria, field design, field implementation and project performance. The in-depth colloidal dispersion gel process is a versatile process that has proven an effective tool in long term enhanced oil recovery programs. Introduction High permeability variation is a problem that adversely affects volumetric sweep in a large number of reservoirs. In heterogeneous reservoirs, the permeability variation normally extends throughout the expanse of the reservoir, so to correct the problem with a gel, large volumes of gel must be placed deep into the formation, not just near the wellbore. If gels are placed near the wellbore to correct in-depth permeability variation, subsequent injection can bypass the gels via vertical crossflow. There are basically two methods of gel injection-bulk and sequential. With bulk gel injection, polymer and crosslinker are mixed at the surface to form a homogenous gel solution, which is then injected into the formation. Sequential injection involves injecting slugs of polymer and crosslinker separately, resulting in the formation of layers of polymer and crosslinker forming on pore walls within the rock. Conventionally, bulk gels utilize high polymer and crosslinker concentrations to form strong gels in the near wellbore area. For conventional bulk gel technology, the high polymer and crosslinker concentrations commonly employed make it uneconomical to inject large volumes of gel to correct in-depth problems. Also, rapid crosslinking reaction rates at high concentrations make in-depth placement difficult. P. 527^