Abstract

Mature oil wells with high water cut suffer from solids deposition with an agglomeration of species like asphaltenes, wax, resin, metal naphthenates, inorganic scale and formation fines etc. Such solids generally accumulate around the well bore, in the production tubing and surface facilities. These deposits can also change the formation wettability towards oil wet. Solid deposition and wettability change create additional resistance to flow in producing wells leading to decline in rate of oil production. Generally in such cases the production decline can be very steep.

Analysis of some deposit samples from such producing wells in Malaysia shows the presence of macro and micro-crystalline waxes, asphaltenes, resins, metal naphthenates, inorganic scale, sand, silt, clay etc. in varying concentrations. The presence of naphthenate deposits is a new problem in many oil wells. The deposition of naphthenates along with other organic and inorganic components create skin and a restriction to flow. This complex gamut of such deposits, especially naphthenates does not dissolve/disperse completely with solvent followed by conventional acid treatment. This often results in acid induced sludges. Use of solvents, acid blends and other composite fluids is reported to remediate such problems with varying degree of success.

To address the deposit problems induced by naphthenates, an effective micro-emulsion consisting of solvents, surfactants, and inhibited acid etc. has been developed to effectively remove organics. The objective of such treatment is to provide dissolution/dispersion of organics that leads to deeper penetration into near wellbore with no sludge formation.

This paper presents laboratory and field data on a treated well from Sarawak which showed significant enhancement in oil production. The well was completed with a gravel screen and exhibited very low productivity from its initial production due to combined completion skin and formation damage. Significant increase of the production rate (from average of 50 bopd to 900 bopd) was observed after the treatment.

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