Limited Entry, Multiple Injection Acidizing Technology Boosts Well Production in the World's Fourth Largest Gas Reserves

stress component and calibrating the stress profiles against ac - tual open hole logs became the most important highlights of the new workflow. Radical improvement of stage integrity, multiple fracture signatures and enhanced well productivity were among the most important results achieved in developing the deep, tight gas-bearing zones of the Khuff carbonate reservoir. Still, an innovative approach was required to address the more prolific zones of the Khuff-C formation where efficient matrix acidizing was sought as an alternative to acid fracturing in wells that could only be drilled in the σmax direction. There - fore, a purpose built open hole multistage technology system — one that was developed around the idea of distributed limited entry for placement of matrix acidizing treatments — was iden - tified and carefully evaluated. This article presents the details of the successful application of this new limited entry, multiple injection technology for opti - mized matrix acidizing of carbonate horizontal wells, including trial testing qualification, candidate selection, system design, functionality, operation and ultimate production profiling. Acid fracturing or matrix acidizing is often required for increased hydrocarbon production and long-term well deliverability from the massive Khuff carbonate gas reservoir in Saudi Arabia, the holder of the world's fourth largest gas reserves. Open hole multistage technologies have demonstrated superior perform - ance in maximizing reservoir contact and productivity through better distribution of acid across the formation matrix, full in - terval matrix contribution and efficient propagation of fracture networks to bypass formation damage and optimize near well - bore conductivity. The Khuff structure is a late Permian age heterogeneous car - bonate sequence that underlies the massive Ghawar field in the Eastern Province of Saudi Arabia. The Khuff reservoir is subdi - vided into four separate intervals (A through D), with production coming mainly from the B and C intervals. Since its initial ap - praisal in the late 1970s, the majority of Khuff development has been focused in the relatively more prolific Khuff-C formation, where coiled tubing acid wash and single-stage acid treatments were repeatedly performed and evaluated. Over the past five years, multistage acid fracturing has been implemented in Saudi Arabia's Khuff-C development. The results were carefully eval - uated for each trial, and this is now the predominant Khuff-C stimulation technique. Up until the middle of 2011, the vast majority of Saudi Ara - bia's horizontal Khuff carbonate gas wells were drilled along the direction of maximum horizontal in situ stress ( σmax ). This was primarily to enhance wellbore stability and achieve the best possible penetration rates. Early multistage fracturing treat - ments in the Khuff generated mostly longitudinal fractures propagating parallel to the wellbore or in the σmax direction. Since then, a holistic approach toward the application of open hole multistage technology for tight reservoir development has been adopted. The complex workflow of this approach calls for, among other requirements, changing the lateral section placement strategy and planning the horizontal section to be drilled along the minimum horizontal in situ stress ( σmin ) direction as opposed to the previous mode of planning along the σmax direction. Ac - cordingly, understanding the reservoir stress profile, orienting the horizontal wellbore with respect to the dominant horizontal