Increasing Production and Injection in Multilateral Horizontal Wells in Naturally Fractured Carbonate Reservoirs by Rigless Intervention—A Case Study, Offshore, Qatar

Abstract

Due to the complexity and cost of stimulating horizontal multilateral wells in an offshore environment, all aspects of this project type must be considered prior to project implementation. Utilizing all technical disciplines to understand the reservoir characteristics and select intervention candidates greatly influences the chance of success for any project. During 2006–2008, 39 wells (19 producers, 17 water injectors and 3 gas injectors) were stimulated in the Shuaiba reservoir in Idd El Shargi North Dome Field, offshore Qatar, resulting in production increases as high as 50% and injection increases as high as 100% in some wells. The wells were stimulated by rigless coiled tubing. A new tool that allows coiled tubing to enter each lateral in multilateral wells was used for these projects. This successful acid stimulation workover program utilized the fundamentals of engineering, geology, geophysics, and petrophysics and applied them with field operations. The screening methods developed led to further workover activity and new drilling development with anticipated reserve and production increases. Introduction Idd El Shargi North Dome (ISND) field was discovered in 1960. ISND is located approximately 55 miles east of Doha, Qatar. ISND is a shallow offshore field, located in water depths ranging between 100 and 150 feet (Fig 1). ISND production is dominated by the Jurassic Arab and Cretaceous Shuaiba carbonate formations, although Jurassic Uwainat (carbonate) and Cretaceous Nahr Umr (clastic) are also developed. Production began in 1964, and Occidental Petroleum of Qatar Ltd. (OPQL) entered into a production sharing agreement with the State of Qatar to operate and develop the field in 1994. The Shuaiba reservoir is the largest of the ISND reservoirs in terms of oil in place but the recovery factor is very low. The Shuaiba reservoir is a densely fractured and highly faulted, low permeability carbonate reservoir. Various well configurations such as single lateral horizontals and multilateral horizontal completions have been used to develop this reservoir. A liftboat unit was contracted in 2006 for data acquisition and rigless stimulation. The successful stimulation campaign explained in this paper is the result of utilizing all technical disciplines to understand the reservoir characteristics for selecting underperforming candidates and designing the stimulation. In this paper, an actual field example is used to show how candidate wells can be identified and how the intervention design can be prepared utilizing a multidisciplinary team effort (geophysicists, geologists, petrophysicists, reservoir and operations engineers). In addition, the paper will explain one technology that can be used to stimulate horizontal multilateral wells without a drilling/workover rig. The methodology described in this paper can be applied to any field that has horizontal and multilateral wells, especially those fields containing naturally fractured carbonate reservoirs. Reservoir Description The Shuaiba formation is extensively faulted and fractured due to domal uplift and regional tectonic events. Shuaiba is a high porosity and low permeability reservoir where large and small scale fracturing has created enhanced permeability regions and pathways in an otherwise tight matrix reservoir. The Shuaiba formation consists of four layers: Shuaiba A, B, C and D and is bounded by two shales: Nahr Umr (above) and Hawar (below). Shale barriers vertically separate the layers, although communication occurs through fractures and faults. Shuaiba A, B, and D are most productive and Shuaiba A is the most prolific, containing the highest percentage of the total Shuaiba oil in place. The Hawar Shale located below Shuaiba D closes the Shuaiba sequence. Immediately below the Hawar Shale is the Kharaib series of carbonate layers. These productive intervals are similar in nature to the Shuaiba D and are in pressure communication with the Shuaiba layers through fractures and faults.

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Assessment of resin systems as solution for well integrity challenge in carbonate reservoirs

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