Removal of Organic Deposits from Oil Producing Wells in a Sandstone Reservoir: A Lab Study and a Case History

摘要

Organic deposit including asphaltene and paraffin may damage the near wellbore area and obstruct production tubings resulting in partial or total loss of well productivity. Most of asphaltene deposits are associated with paraffin. This paper presents a first successful field application of a lab proven/optimized chemical solvent to remove organic deposits from a dead oil well in a sandstone reservoir. 　　A vertical gravel-packed oil producer well was dead due to deposition of organic material in 3?” production tubing forming obstruction to flow. The deposition is expected to take place due to long shut-in time as experienced in this well with high GOR. A bailer samples was obtained from this well. Analysis of the obstructing material indicated that they were mainly asphaltene associated with paraffin. Solubility of obtained organic deposits in several solvents was evaluated at reservoir temperature (188°F) and monitored as a function of soaking time. 　　Several criteria were considered in selecting of the optimal solvent formulation, among which were safety and solvency power. The selected formulation incorporates asphaltene dissolver solvent and paraffin dissolver solvent in addition to surfactant. Application of the optimal solvent formulation, that exhibited the maximum solvency power in a minimum soaking time, was very effective in restoring well productivity while minimizing operational cost. A total of 12 feet of obstructing organic deposits were removed from the production tubing using coiled tubing in a multi-stage treatment. Following, the solvent was squeezed into the formation across the screens to maximize cleaning efficiency at the source. The sustainable oil production rate obtained and asphaltene content in flow back samples indicated that the treatment was very successful. To prevent further asphaltene/paraffin precipitation during shut-in time, asphaltene/paraffin inhibitor is recommended. A detail of asphaltene/paraffin formation mechanism, lab evaluation and field application results will be addressed.