Encapsulated Scale Inhibitor for Use in Fracturing Treatments

Abstract

This paper describes the development and testing of a solid, encapsulated scale inhibitor for use in fracturing treatments. Data from laboratory and field tests are reported. Laboratory testing with a continuous flow apparatus has yielded inhibitor release rates under dynamic conditions. The inhibitor was tested to determine the minimum inhibitor concentration required to inhibit the formation of CaCO3, CaSO4, and BaSO4 scales in brine. Laboratory data were used to determine the parameters of a mathematical model to predict the long-term release rate of the inhibitor. Data from a treated well are compared with predictions of the model. Release-rate testing in a continuous-flow apparatus shows that an encapsulated solid derivative of a phosphonate inhibitor has a sustained release profile. Temperature (100 to 225 F) and brine strength have a small effect on the release-rate profile. Coating the solid derivative makes it compatible with metal-crosslinked fracturing fluids. The coating has a short-term effect on the release-rate profile. The composition of the solid derivative has the greatest effect on its long-term release-rate profile. A comparison between the mathematical model proposed to describe the long-term release rate of the inhibitor and actual data collected from a treated well shows a large discrepancy, likely because most of the inhibitor is not in contact with the water being produced from this well. Introduction A variety of scale inhibitors are available for use in oilfield applications, including polyphosphate phosphate ester, phosphonate polyacrylic acid, and polyacrylic acid derivative inhibitors. Most of these inhibitors are available as liquids and can be applied by continuous addition or in squeeze treatments. Polyphosphate inhibitors appear to be one of the few types available in a solid form that can be combined with a hydraulic stimulation treatment. A solid inhibitor that can be applied in conjunction with a fracturing treatment allows two treatments to be combined, saving the operator time and possibly expense. The objective of this paper is to describe our work in developing and testing a solid scale inhibitor for use in fracturing treatments for wells with BHSTs up to 225 F. Several inhibitors were screened before three candidates were chosen. These three inhibitors were tested to determine (1) their effectiveness to inhibit commonly occurring oilfield scales and (2) their release-rate profiles in continuous flow-release experiments. A mathematical model was used to describe the release-rate profiles and to predict the long-term behavior. Compatibility testing showed that solid derivatives of these inhibitors interfered with metal-crosslinked fracturing fluids. To abate this interference, a semipermeable membrane was used to coat the solid derivatives. The following data is presented for the solid derivative chosen for field testing:–effect of the coating on a release-rate profile–effect of brine strength on a release-rate profile–minimum effective dosage of inhibitor required to inhibit scale formation for calcite, gypsum, and barite scales Results for one field trial are reported and compared to the mathematical model. Experimental Equipment. The test system used to determine the release rate of inhibitors is shown in Fig. 1. The system consists of an isolated reservoir of brine that supplies the test column. The reservoir is made from Ampcoloy, and all tubing in the system consists of stainless steel or nylon tubing. Several 12-in. columns of 0.75-in. OD stainless tubing were used for testing. Nitrogen was used to maintain the system pressure at approximately 200 psi. P. 557

First Application of Scale Inhibitor During Hydraulic Fracturing Treatments in Western Siberia

“…Scale prevention can be accomplished by using scale inhibitors [6][7][8] . The common oilfield scale inhibitors used by the industry are phosphorous compounds or polymers such as organo-phosphonates, polyacrylamide and polyacrylate.…”

Scale inhibitors

“…This type of scale inhibitor allows chemical release over an extended period [62,63]. Microencapsulated formulations may contain a gelatin coating with a multipurpose cocktail, such as [44,64]:…”

Fracturing fluids

“…A solid, encapsulated scale inhibitor (calcium-magnesium poly(phosphate)) has been developed and extensively tested for use in fracturing treatments [152][153][154]. The inhibitor is compatible with borate-crosslinked and zirconium-crosslinked fracturing fluids and foamed fluids because of coating.…”