Sand Production Control by Accelerated Low-Temperature Oxidation

A research group in the Department of Petroleum Engineering, KFUPM, developed a new method for sand control in sandstone oil reservoirs whose rocks are poorly consolidated. The patented method (US 6,364,019 B1, granted April 2, 2002) involves saturating the sand matrix around the wellbore with a consolidating solution, which is a hydrocarbon formulation with a high asphaltene content. Air is then injected into the sand matrix to oxidize the solution at the reservoirs temperature. The low-temperature oxidation (LTO) reaction results in the deposition of a thin film of coke-like resinous material on the sand grains that bonds them together and creates a permeable consolidated sand matrix. This low-cost method was proven successful in a physical wellbore model, built to scale, and was subsequently tested on an oil well in a Saudi Arabian field. A key requirement in the consolidation process is the fast accumulation of heat within the treated volume of the wellbore region caused by the LTO reaction, which would carry the process to completion. For relatively cold reservoirs, the LTO reaction needs to be accelerated by preheating the wellbore of the well to be treated through steam injection or by downhole heaters. Both options are time consuming, incur added cost, and may prove unpractical in some cases. Thermochemicals have been used in a variety of applications in the petroleum industry such as cleanup of sludge from storage tanks and removal of wax deposits from wellbores. They have also been proposed to induce multiple fractures within the matrix of tight gas reservoirs. A typical formulation involves mixing aqueous solutions of two compounds whose exothermic reaction generates a substantial amount of heat. The objective of this proposal is to investigate the feasibility of employing thermochemical reactions to preheat the wellbore area to be treated by the sand control technique described above. experiments will involve a sample of loosely-packed sand housed in a vessel. After saturating the sand pack with one chemical, the thermochemical reaction will then be triggered by injecting the other chemical causing the sand packs temperature to rise instantaneously. The consolidating solution will then be injected into the hot sand pack followed by continuous air flow to oxidize the solution in situ. Should the rise in the sand packs temperature be found insufficient, a second cycle of thermochemical treatment will be administered before injecting the consolidating solution. Several parameters will be investigated with the goal of optimizing the process to produce a consolidated sand pack with a high compressive strength and adequate permeability. Such parameters will include the type and concentrations of the thermochemicals, the number of preheating stages, the duration of air flow, and, probably, the grain-size distribution of the sand pack. If successful, this pre-heating technique will extend the applicability of the sand control method to cool and shallow sand-producing oil reservoirs in Saudi Arabia and elsewhere.