Laboratory Studies and Field Evaluation of a New Gelant for High-Temperature Profile Modification

Abstract

Abstract This paper reports the laboratory development and initial field testing of FLOPERM 325, a novel gelant for high temperature profile modification. The new gelant is a synthetic, thermosetting material which can be used at concentrations of about 1-2% in injection brines. Its gelation rate can be controlled over the range of several hours to about 10 days at temperatures of up to 221 deg. F (105deg.C), permitting emplacement at varying distances from the injector wellbore. In sandpack testing to simulate gelant performance under reservoir conditions, the new system reduced permeability to brine by more than 90% while retaining most of the original permeability to oil. Moreover, in parallel sandpack tests permeability to oil. Moreover, in parallel sandpack tests the gelant selectively reduced permeability in the zone with higher initial permeability. Emplaced gels have retained functional stability in sandpacks for more than ten months at 197deg.F (92deg.C). An injector well test of the gelant was performed at ARCO's Nelson Minnelusa Unit ((197deg.F (92deg.C), in Campbell County, Wyoming)) in March, 1984. A 2000-bbl solution was emplaced in the formation over a two-and- one-half day period. Injection profiles showed diversion of injection brines from a water channel to the oil payzone. Enhanced oil recovery and decreased water cut payzone. Enhanced oil recovery and decreased water cut were observed within several months of the treatment and are continuing. Introduction Profile modification is a means of enhancing oil recovery Profile modification is a means of enhancing oil recovery by diverting flood water into previously underswept zones. The method comprises emplacement of a gelant slug into the highly-permeable, flooded-out layers of the formation proximate to the wellbore. The gel is designed to reduce proximate to the wellbore. The gel is designed to reduce the permeability of the target zone to the flooding fluid, thereby modifying the flow profile and diverting injected fluids into zones of greater residual oil content. The design of the gelant treatment — i.e., quantity of material injected, depth of emplacement, gel performance, etc. — is a function of the specific performance, etc. — is a function of the specific characteristics of the reservoir and the applicable gelant system. The concept of profile modification can also be applied to producer wells to suppress coning of water or gas and to increase oil production by controlling the water or gas cut.' Moreover, the concept of profile modification can be applied to steam,' CO2 and gas- miscible floods. The utility of profile modification using metal-cross- linked polycrydamide and xanthan gel systems is well documented Polyacrylamides crosslinked with either Cr(III) or AI(III) are widely, used with injection brines of low salinity and hardness. Xanthan crosslinked with Cr(III) is employed over the entire range of salinity and hardness encountered in the field because of the relatively insensitivity of xanthan to both salinity and hardness. Profile modification is characterized by low treatment Profile modification is characterized by low treatment costs, quick response time, low risk, and frequently favorable payback. The effectiveness of polyacrylamide and polysaccharide gel stems in reservoirs with temperatures above about 160deg.F (71deg.C) is questionable because of thermal instability of the gels. These performance limitations are believed to be due, at least in part, to the ionic crosslinking of the gels. The need for gelants that can be used at elevated temperatures prompted the search for novel systems based on covalent crosslinking chemistry. Numerous diverting agents have been reported in the literature, some for high-temperature applications targeted for diversion of steam as well as water. These materials range from low-molecular weight monomers to polymers which are ionically or covalently crosslinked polymers which are ionically or covalently crosslinked either during or following emplacement in the reservoir. Generally these systems function over limited ranges of temperature, salinity and pH.