Mechanical descaling of iron sulfide scales in high angle non-monobore or horizontal open hole completion offer multifaceted challenges, especially when the reservoir is depleted. The history of the descaling program in carbonate gas wells in Saudi Arabia dates back to 2007. The program suffered several setbacks with operational complexities like stuck pipe, H2S generation (souring) during chemical dissolution and severe induced damage during reservoir isolation process. The depleted reservoir needs to be isolated to ensure full circulation during mechanical descaling process. The mechanical means of isolation with a bridge plug is not feasible due to the presence of FeS scale in the wellbore. The only isolation option available at the moment is CaCO3 chips bullheaded from the surface. Often the post-descaling and stimulation operation does not restore the original production, due to the heavy damage induced in the reservoir during isolation. This paper shares a successful descaling experience and best practices in a single lateral open hole well that was completed with 4-1/2-in tubing and 7-in liner, and had severe pressure depletion. A novel non-damaging visco-elastic surfactant based fluid was used to fill the open hole lateral and as base to support CaCO3 chips above it that prevented additional damage and allowed reservoir isolation for mechanical descaling, using high pressure coiled tubing and a jetting tool. A clean wellbore with no further induced damage made subsequent post-stimulation results very attractive. The paper also presents the production results of stimulation treatment performed after the descaling treatment.

Completed with 4.5 in tubing and 7 in Liner, the upper carbonate reservoir had previously been stimulated and produced until reaching its economic potential. To prolong the well life, the decision was made to permanently isolate the upper zone, then perforate, matrix stimulate and produce from the lower zone.The challenge for this operation was that the existing upper zone had been stimulated, creating a large void behind the casing with known high fluid loss. It was determined that isolation with cement would have only a small chance of success due to the high leak-off in the previously stimulated reservoir. Also, this zone was at a 40° inclination, making it more difficult to place an uncontaminated cement plug with Coiled Tubing (CT) and clean out the cement after placement.An inflatable packer was also considered to isolate the upper zone and perform acid stimulation on the bottom zone. The bottom-hole pressure and temperature (5,000 psi and 300°F) were beyond the operational limits of any inflatable element available in the region.For this unique situation, a new method was designed and successfully implemented. The new approach included first filling the upper zone with calcium carbonate chips (CaCO 3 ) to reduce or limit the fluid losses. Then, utilize CT to place a chemical isolation treatment. The product utilized was an organically cross-linked polymer (OCP) system capable of permanently sealing the target zone by forming a 3D rigid gel. It is effective for preventing water and gas flow in sandstone and carbonate formations from 100°F to 350°F (38°C to 177°C). A benefit of the treatment was the ease at which it could be pumped and placed via CT and then cleaned out. All that is required for cleaning is a nozzle and jetting action. The implementation of this chemical sealant procedure provided reliable zonal isolation of highly depleted upper zone and allowed full access (with CT, Slick Line and E-line) to deeper productive lower zone. The successful chemical isolation in this well has resulted in avoidance of expensive workover operations.This paper discusses the pre-job planning, benefits, challenges, design, execution, evaluation and lessons learned for applying this novel isolation method.

Video cameras have been used in the oil industry with high success rate reported by several operating companies around the world. However, High downhole temperatures especially in gas wells have always posed a limitation to the full utilization of the camera as a diagnostic tool. Previous trials with the camera were prematurely aborted as internally it tends to heat up quickly allowing no time to carry out the full diagnosis of the restriction. However since the camera has gone through extensive modifications and has been equipped with the necessary capabilities to withstand high downhole temperatures. Picture resolution, re-fresh rate, LED intensity and tool rotation can be controlled at surface by the operator. Well deviation, high side and internal tool temperature are among the parameters displayed at E-line Cabinet on surface. This paper documents a successful operational experience of the first HT run in Saudi Arabia using this type of downhole camera. E-Line High Temp camera was deployed in gas well in attempt to determine the cause of an unpassable obstruction. Several measures to diagnose the nature of this obstruction were attempted using series of gauge cutter runs but with no success. The High Temp camera was mobilized in an attempt to finally discover the severity and extent of this obstruction. The operation using the downhole camera was carried out successfully achieving the desired objective of the intervention. The interpretation of the images indicated that the well had some kind of mineral build-up which looks to be solid in appearance indicating scale or cement materials.