In-Situ Sand Consolidation by Low-Temperature Oxidation

Abstract

Abstract Low-temperature oxidation (LTO) of crude oil has been employed to investigate its potential as a sand consolidation technique. Loose sand (20/30 mesh) saturated with crude oil (18 – 20 API) and brine was subjected to air injection at a low temperature (100 – 150 C) for a period of time (6 – 18 hours). The sand packs developed compressive strengths ranging between 375 and 1264 psi and suffered a maximum permeability loss of 22%. It was found that higher oxidation temperatures reduced the consolidation time and increased the compressive strength; but had no effect on the magnitude of permeability loss. Heavier oils required less oxidation time, caused slightly larger permeability losses, but had an insignificant effect on compressive strength. The presence of clay enhanced the LTO reactions by shortening the oxidation time and increasing the amount of residue deposited on the sand grains. This greatly increased the compressive strength, but at the expense of larger permeability losses. When interstitial water was present with clay, the permeability loss was increased further while the compressive strength was slightly reduced. Acid treatment had no effect on the residue deposited on the sand grains. Experimental testing as well as two predictive models showed that this technique provides sufficient compressive strength to withstand sand-free, high flow velocities and results in much smaller permeability losses compared with plastic consolidation. Introduction Sand production is considered to be one of the major operational problems in producing poorly consolidated reservoirs. Sand influx into the wellbore may lead to various problems such as erosion of valves and pipelines, plugging the production liner and sand accumulation in the separators. Cleaning and repair works related to sand production plus loss of revenue due to production rate restriction amount to great costs incurred by the industry every year. Furthermore, undetected erosion of production equipment may pose a major safety hazard in case of high-pressure gas wells. Therefore, sand control has attracted much research effort for more than six decades. Several methods are commonly used to prevent or reduce the flow of sand particles into the wellbore during the course of production. These methods use either mechanical means (sand screens, filters, perforated or slotted liners, gravel packing) or chemical agents (plastic consolidation). Certain completion and production practices are also employed to minimize or prevent sand production. Most existing sand control methods have their own drawbacks. In the mechanical methods, the setting of liners and gravel packing around liners may require a long time which adds to the cost. Moreover, the formation sand is still free to move and hence may plug the gravel pack or liner. In the chemical methods, some difficulties may arise in achieving polymerization of the injected resinous material in the formation - to consolidate sand particles - and still maintain adequate permeability. Furthermore, these resinous materials are proprietary and quite expensive. All these drawbacks leave a substantial and unfulfilled need for a sand control method capable of effectively preventing the flow of sand particles into the wellbore. Low-temperature oxidation of oil had been experimented with as a means of in-situ consolidation of sand. In this paper, the results of a new form of this process are presented. Low Temperature Oxidation Crude oils react with oxygen through numerous and complex reactions. These reactions have been found to fall into distinct categories depending on the reaction temperature. At temperatures below 500 F, the low temperature oxidation (LTO) reactions are dominant, and produce mainly oxyginated hydrocarbons such as alcohols, aldehydes, ketones, acids and hydro-peroxides with little carbon oxides. P. 547