Abstract
Formation damage associated with water blockage is a common problem in oil/gas producing wells. Water blockage is a damage mechanism which occurs when water saturation increases near wellbore, resulting in reduced hydrocarbon saturation and relative permeability to gas. When pore spaces around the well get nearly saturated with water, it reduces gas saturation to near irreducible level that block the gas flow. It decreases the gas production and may recover naturally by extended flow back or excessive drawdown. However, in depleted reservoirs, gas production may completely be lost and shall require chemical treatment. In this paper, a case study has been presented illustrating the complete loss of production of a gas well owing to the water blockage and the treatment mechanism to restore the production (SPE 102383).
Well ‘A’ was drilled in Sindh, Pakistan in 2010 in Lower Goru Formation. Later, the well was put on compression and was found on natural decline. By Feb 2019, well was producing 1.14 MMSCFD gas, 6 BPD condensate, and 43 BPD water with 123 psi FWHP. In March 2019, well was shut-in for the pressure build-up (PBU) survey. However, when the well was opened to flow, there was complete loss of production.
Identification of the causes of production loss was a major challenge in designing the job. After analysis of well behavior, gradient survey data and formation properties, it was found that the loss of production was attributed to water blockage caused by prolonged exposure of water.
Based on above analysis, a stimulation treatment using Volatile Acid System was designed to address the water blockage. The improved cleanup with volatile acid can be expected for two reasons; (1) increased volatility and (2) lower surface & interfacial tensions (SPE-191292-MS). The increased volatility results in lower water saturation and improving relative permeability to gas. Volatile acid system lowers the surface tension and increases the vapor pressure (gas saturation/relative permeability of gas near the damaged zone) and improves the clean-up of spent acid and retained water. In addition, presence of alcohol in acid system helps in achieving deeper penetration into the rock matrix. The proposed solution of Volatile acid system proved successful not only in reviving well's production but also with a gain in production of about 300%.
