Making Workovers Easy and Cost Effective: Turning Old Ways into New Opportunities

A case study and methodology is presented to shed the light on the different processes followed during the placement of a non-damaging isolation barrier in a group of highly naturally-fractured and vugular gas wells. The temporary isolation aims at isolating the wellbore from the troublesome formation and allow the removal of the original completion string and install a new redesigned one. The process helped putting the wells back on production with-out the need to stimulate any of them. This helped client to reduce the overall workover cost by 40% and proved to be successful and efficient to complete the required operation in a time-efficient.

The operator had 4 wells with OH sections ranging from 40-80m which were completed in the late 1990's with no production packer. To preserve wellbore integrity the completion string needed to be pulled and replaced by a string with production packer and DH gauges. Visco-Elastic Surfactant (VES) and calcium CaCO₃ (carbonate) used ubiquitously in field operations were tested for optimal design to fill highly fractured OH without damaging formation. Caliper logs were not available, and the presence of natural fractures posed a challenge to calculate the actual OH volume. A system was developed to carry the CaCO₃ into the wellbore in stages and slickline was employed to measure fill after each stage. Once the OH was filled with CaCO₃ and well would support a fluid column coil tubing was used to place an acid-soluble cement plug in the short interval between casing shoe and end of tubing (6-9m). The paper describes the optimization process followed to tune the CaCO₃ pads composition, gel composition, mixing and placement technique.

The first well in the campaign required more than 10 times the theoretical volume of CaCO₃ to fill the open hole with multiple settling issues at surface. It was concluded the surfactant gel was likely carrying the CaCO₃ into the fractures. The procedure was modified to tie in a line of breaker solution to the well head allowing sufficient viscosity of the fluid to carry the CaCO₃ from surface but immediately lose viscosity and allow the CaCO₃ to settle in the open hole without being carried into the formation. Specific coil tubing procedures were employed to allow the setting of ultra-short acid soluble cement plugs (<6m).

All wells were successfully isolated to allow the safe workover of the completion string and returned to production with no loss of gas flow, with-out the need to stimulate after the work over.

The campaign exhibited a new method of employing existing technologies to achieve the objective in a highly challenging and relatively new oilfield of Kurdistan. The campaign also demonstrated the benefit, in terms of saving time and cost because of extensive pre-execution planning.