Sand production from a poorly consolidated reservoir formation is always considered a challenging problem in the petroleum industry. Sand production can cause erosion and corrosion to downhole and surface equipment and loss of production. Over the past few decades, sand control techniques have attracted increased attention to improve and enhance the characteristics of weak sand formations. Enzyme-induced calcite precipitation (EICP) is considered a relatively new sustainable technique studied for soil improvement. In-situ calcite precipitation in the sand can restrict the movement of the grains by forming bridges. This precipitation fills the pores and binds sand particles causing a reduction in the porosity which as a result improves sand shear strength.
In this study, different mixes of EICP solution were studied and tested in the laboratory. To cure the samples at higher temperatures Xanthan Gum (XC-polymer) was used as a temperature stabilizer. EICP solution is primarily composed of urea, calcium chloride, magnesium chloride, XC-polymer, and urease enzyme. Different concentrations and compositions of reagents were tested. The mixed solutions were left for different curing times at different curing temperatures to allow the reaction to happen. The properties of the produced precipitates were examined through different techniques such as pH, conductivity, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and Thermogravimetric analysis (TGA).
The XRD results showed the precipitation of calcite and dolomite. The combination that produced the highest amount of thermally stable calcite with a minimal amount of aragonite, highest precipitation efficiency was further selected for the sand consolidation experiment. A solution containing 1M Urea, 0.5M CaCl2, 0.5M MgCl2, 5g/L XC-polymer, and 2g/L urease was considered as an optimum combination for an EICP process.
The novelty of this paper is that it not only describes the development of a unique formula for the EICP process used for sand control and water conformance but also provides a selection criterion for applying the EICP for these downhole applications.