Achieving good zonal isolation in wells characterized by lost circulation has been a challenge in the Wafra field of Kuwait. The field is characterized by highly fractured formations with very low fracture-pressure gradients. In the Wafra field production intervals were commonly drilled with partial or complete losses, causing risk during drilling and cementing operations and damaging the producing formation. Also, uncemented columns of casing have developed leaks as a result of corrosive formation fluids. Two-stage cementing with extended slurries and top jobs were the common practices in this field in an attempt to circulate cement to surface. This technique delays the drilling progress, and the low mechanical properties of the extended slurries do not provide the required zonal isolation. A new cementing program was introduced to combat lost circulation in this field. A slurry technology at a density of 900 kg/m3 (7.5 lbm/galUS) was used to cement the low-fracture-gradient production zone without cement losses or formation damage. Excellent set cement mechanical properties were achieved with very low set-cement permeability. In wells where high losses were expected, a surface-treated fiber was added to the cement to bridge across the problem zone. This paper presents case histories study of several wells, laboratory designs, and field data in which these new techniques successfully treated partial to complete losses encountered during cementing operations. In all jobs using the new slurry, lost circulation problems were cured and cement was circulated to surface. Introduction Fighting lost circulation is a costly and time-consuming process. Excessive costs can result from drilling/completion fluid and cement losses, and rig time is added for multiple stage cement jobs and possible remedial well work. Lost circulation can also have other consequences including stuck pipe, well control incidents and formation damage because of fluid loss to the production zone. Curing these problems is critical if the operator is to control the well and drill and complete it effectively. There are numerous lost-circulation techniques in the industry, and the common objective is to contain the losses before proceeding with cementing operations. Some of the traditional treatments for these scenarios are lost circulation material (LCM) or spotting cement plugs in the open hole during the drilling phase. However, there are numerous cases in which losses are encountered just before or during cementing operations. Lost circulation can cause the primary cement job to fail, which not only increases well costs but also jeopardizes well integrity and well life. Experiencing losses during cementing can result in poor zonal isolation caused by poor cement coverage or low top-of-cement, requiring additional casing strings and/or top-up jobs as well as subsequent workovers. Background Typically, the stratigraphy for wells drilled in the Wafra field includes the shallow Kuwait series sand, which is comprised of loose sandstone from surface to a depth of about 61 m (200 ft). Deeper, the Dammam formation consists of a naturally fractured limestone interbedded with chert and dolomite (Fig. 1). The Dammam is moderately hard at the top and grows softer towards the bottom. Between Dammam and Maestrichtian formations are the first and second Eocene formations starts from 320 m to 640 m (1,050 ft to 2,100 ft) and consist mainly of dolomites interbedded with limestone, anhydrite and gypsum. Alternated with the Eocene formations are hard and sometimes massive anhydrites with dolomite and gypsum streaks. Next, extending from about 732 m to 1,037 m (2,400 ft to 3,400 ft) are the first and second Maestrichtian formations, medium to hard fractured limestone and dolomite with shale streaks.
In the recent years horizontal well technology evolved in the Middle East field development strategies becomes favored over vertical and deviated wells offering the advantage of maximized reservoir contact, higher production rates and better access to reserves. However, most of these horizontal wells are completed openhole with little alternatives for stimulation, water shutoff or workover treatments. A very challenging task to stimulate long openhole sections effectively due to poor acid distribution especially in reservoirs with high permeability streaks that require effective diversion techniques. The efficiency of chemical diverting agents in terms of flow distribution and uniform coverage is limited when it comes to treat such complex wells with long openhole intervals (see Fig. 1).This paper illustrates a case history where an innovative technique was used on stimulating a naturally completed horizontal well that experienced a production drop to zero shortly after the completion in 2004 due to formation damage and incomplete cleanup. This technique combined mechanical and chemical diversion, using selective openhole completion allowing the wellbore mechanical segmentation into six small intervals based on petrophysical and reservoir evaluation, so that the selected sections can individually be stimulated evenly and inflow contribution from the entire openhole section can be maximized win one continuous operation.The treatment used the advanced emulsified acid technology to achieve deep penetration and better etched fracture conductivity. Viscoelastic surfactant self-diverting Acid (VES diverting acid) was used as the chemical diverter to assure good zonal coverage across each stimulation stage. Greatly increasing the effectiveness of the treatments the combination of technologies allowed successful stimulation of the well with 20:1 permeability contrast. The last stabilized measurement indicates sustained natural production of 10,000 bopd, which is five times the field average and three times greater than the best well in the field without requiring artificial lift. BackgroundWith more than 8% of world reserves Kuwait is blessed with an abundance of oil. However, oilfield operators recognize that there are many fields where the recovery of the resources are more challenging and required the use of advanced technologies. One of the flagrant examples is the challenging Mauddud formation in the Sabriyah field in Northern Kuwait, where in the last decade a couple of attempts at drilling horizontal oil producer were mostly unsuccessful and showed very disappointing production figures, with higher than expected production of unwanted fluid and completion costs. Since the oil could not be recovered economically, work to develop these reservoirs was suspended for not saying abandoned.In 2006, Kuwait Oil Company (KOC) contracted the service company to revisit this problem and determine if the technology had been invented which would allow this suspended reservoir to be developed and achieve the planned field product...
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMost of the wells in Sabriya Field (Northern Kuwait) produce from reservoirs, where multiple layers are opened to production. Problems related to non-desired water production are drastically affecting the oil production, and have been an ongoing concern. The exclusion of this water represents a challenging task by itself especially in case of multiple zones interval simultaneously producing, and where completion of the wells restricts considerably the convoyed down-hole tools configuration This paper covers water shut off case history of an oil producer that has shown according to the production data an increasing water production figures. The nature of water problem and the fact that the targeted section is located inbetween multiple oil producer zones revealed the necessity of a complex thru tubing zonal isolation solution before performing the water shut-off treatment. Temporary coiled tubing conveyed straddle system was created using two thru tubing inflatable packers, isolating the top and bottom perforated zones in order to provide both proper zonal isolation and accurate treatment placement. The post water shut off treatment showed up to 70% water flow reduction from the targeted layer has been achieved.
Dual completed wells producing from the mature carbonate formation in northern Kuwait are encroached by injected water from adjacent wells presenting a challenge for the operating company. Greater oil demand coupled with limited surface water handling facilities increased the importance of stimulating this type of challenging wells due to the drastic permeability contrast across the pay zones. Typically the treating fluid in a matrix treatment flows into high permeability sections and/ or high water saturation "thief zones" resulting in higher water cut due to the over stimulation of the water zones instead of the oil bearing zones. The objective of the present field case study was to place the stimulation fluid equally throughout all intervals of the oil bearing layers while temporary protect the zones suspected to be mainly contributing with water from the stimulation fluid, using two different types of viscoelastic surfactant (VES) polymer free diversion systems placed with coiled tubing (CT) providing effective plugging of the layers producing water and providing a uniform stimulation fluid coverage across the entire pay zone. Subsequent production rates showed substantial oil production increase and water production decrease, 360% and 40% respectively. Background In the Sabriyah field of northern Kuwait, the wells are usually completed with a dual completion string which provides the mean to access both Mauddud carbonate formation and underlaying Burgan sandstone formation (see Fig. 1). Mauddud formation is a thin low permeability carbonate layer with an average permeability of 20 md and porosity of 22%. The formation contains large amount of natural fractures and produces 23–25º API gravity oil. Due to the lack of nature water influx, the formation has been under water flooding since 1997 in order to sustain the reservoir pressure and field production. However, water breakthrough becomes an issue as soon as the water flooding was started. This is confirmed by the production logging results. Once the water is broken through those high permeability streaks or natural fractures, the oil production rate is dropped dramastically. The formation damage like organic deposits and scales has also contributed to the decline of oil production. The ideal solution would be shut off the water breakthough intervals and then stimulate the oil bearing intervals only. However, conventional isolation tools and stimulation techniques will not work in this case because the Mauddud formation is usually completed in the short string. It is quite challenging to isolate the water intervals and place the stimulation fluids precisely into the oil bearing intervals unless the entire completion is pulled out and each particular interval can be accessed seperately by using a straddle packer. This approach will not only involve the workover rig but also impact the production from the lower Burgan sandstone formation, as well as formation damage associated with the workover operation. Several wells were treated with this approach in the past, but the results showed not to be very cost effective considering the complexity of the operation as well as the production loss from the lower Burgan formation during the workover. Thus an engineering solution of stimulating oil bearing intervals but avoiding suspected water breakthough intervals with the current completion in place is highly required.
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