Field Evaluation of a New Gelant for Water Control in Production Wells

Abstract

A new chemical process for improving the performance of wells producing at high watercuts has been developed. This process is based on covalently bonding a medium molecular process is based on covalently bonding a medium molecular weight, cationic polyacrylamide with an organic crosslinking agent to form a three dimensional gel structure. Because the gel solution is hydrophilic, it is preferentially emplaced in the zones of high water saturation and high water permeability. Gelation rate is controlled by adjusting the permeability. Gelation rate is controlled by adjusting the pH of the gel solution. Once the gel structure has pH of the gel solution. Once the gel structure has developed, effective water permeability is reduced with little impact on the effective oil permeability. This paper reports on the results of over 30 wells treated using the new process. Substantial decreases in water production have been realized and, in some cases, production have been realized and, in some cases, significant amounts of incremental oil recovered. The evaluation of these treatments helps demonstrate the working mechanisms of the gelant and the optimum field application of the process. Introduction Excessive water production is a common oilfield problem. In recently completed wells, the payout of drilling costs and related capital investments can be adversely affected by large amounts of water production. In older wells, water lifting, treatment, and disposal costs can shorten the economic producing life, resulting in abandonment and loss of recoverable reserves. Generally, water production results from coning or channeling. Coning, a near-wellbore phenomenon, occurs when the pressure gradients causing fluid flow overcome the differential-gravity gradients between the oil and water. High vertical permeabilities can accelerate the effect. Channeling occurs through fractures or high permeability streaks. The source of the water can be an underlying aquifer or water injection wells. Conventional techniques to control water production include mechanical zone isolation (if possible) or cement squeezing of the water-bearing zone followed by reperforating uphole. Uncrosslinked polymers have also been used with some success. Gels and other chemical systems investigated in the past decade have been thoroughly reviewed in a recent paper, containing an extensive reference list. The goals of a production well gelant treatment are to reduce water production and, if possible, to increase oil production. In situations where water disposal costs are production. In situations where water disposal costs are high, it may not be necessary to achieve incremental oil in order to pay out the treatment In the majority of cases, however, increased oil production is required for treatment payout in a reasonable amount of time. After considering payout in a reasonable amount of time. After considering the goals of a treatment and the state of the art associated with existing technologies, the following objectives were established for the development of an improved gelant.–The gel should be selective in reducing permeability to water while having little effect on oil permeability. Thus, even if gel enters oil producing zones, minimal reduction of net oil production would result.–The gel should be versatile enough to control water in matrix rock as well as in fractured reservoirs. P. 203

Effects of divalent cations, seawater, and formation brine on positively charged polyethylenimine/dextran sulfate/chromium(III) polyelectrolyte complexes and partially hydrolyzed polyacrylamide/chromium(III) gelation

“…1,2 Historically, the most common blocking agent used for water shutoff and sweep improvement is partially hydrolyzed polyacrylamide (HPAM), in which a fraction of the amide groups are hydrolyzed to form negatively charged carboxyl groups and which can be crosslinked with a polyvalent cation, most often Cr(III), to form a gel. [3][4][5][6][7][8][9][10] A solution of HPAM is mixed with Cr(III) [typically, 5000-ppm HPAM and 100-ppm Cr(III)] and injected into the formation, where it invades the highest permeability spaces and sets in place. [8][9][10][11] To maximize the depth of placement of the gelant, it is desirable to have a long gelation time because, once set, the pressure required to continue propagation into the formation may not be attained because of limitations imposed by the hydraulic conductivity, parting pressure of the rock (the pressure at which the rock fractures, which further increases the hydraulic conductivity), and available pumping capacity.…”

Comprehensive Review of Polymer and Polymer Gel Treatments for Natural Gas-Related Conformance Control

“…Dovan and Hutchins [ 34 ] applied hydroxypropyl guar (HPG) crosslinked with titanium chelate [ 53 ] in treating excess water in Northern California gas wells. Two techniques were adopted in the field deployments to selectively reduce the water permeability and maintain the gas productivity.…”

Fluid diversion and sweep improvement with chemical gels in oil recovery processes. Final report

“…In an earlier investigation, we studied how fi)ur different gels reduced permeability to water and compressed carbon dioxide in Berea sandstone (see pages [34][35][36][37][38][39][40][41][42][43][44]. That investigation raised several issues we address in this section.…”