Summary Effective matrix acidizing in Kuwait's horizontal openhole wells is a big challenge. Reservoir heterogeneity and the length of the horizontal wells make acid placement and diversion difficult, particularly in high-water-cut (WC) wells in which water has broken through as a result of high-permeability streaks or natural fractures. Furthermore, acid penetration is limited by the large surface area of the horizontal wellbore, and this is exacerbated by the relatively small injection rate imposed by the use of coiled tubing (CT). To make matters worse, formation damage in horizontal wells is usually very deep as a result of long exposure times. This paper discusses the application of a new viscoelastic-surfactant (VES)-based, self-diverting acid system for stimulation of more than 20 horizontal openhole wells in carbonate reservoirs in Kuwait. The application also deployed a new nonparticulate material that forms a highly viscous plug when it contacts water and that degrades when mixed with oil in the formation. The new fluid system is pumped before the acid treatment to effectively prevent the acid from stimulating high-water-saturation sections. The field results show significant improvement in post-stimulation production, owing to effective diversion and water-production control compared with wells in which a conventional polymer-diversion technique was used in the past with no consideration for water-production control in high-WC cases. The new technique has been selected as the standard stimulation practice in most horizontal openhole carbonate wells in Kuwait.

Effective matrix acidizing in Kuwait's horizontal openhole wells is a real challenge. Reservoir heterogeneity and the length of the horizontal wells make acid placement and diversion difficult, particularly in high water-cut wells in which bottom water has broken through high permeability streaks or natural fractures. Furthermore, acid penetration is limited by the large surface area of the horizontal wellbore and is exacerbated by the relatively small injection rate imposed by the use of coiled tubing. To make matters worse, formation damage in horizontal wells is usually deep due to long exposure times. This paper discusses the application of a new viscoelastic surfactant-based, self-diverting acid system for stimulation of more than 20 horizontal openhole wells in carbonate reservoirs in Kuwait. The application also deployed a new non-particulate material that forms a highly viscous plug when it contacts water, and degrades when mixed with oil in the formation. The new fluid system is pumped prior to the acid treatment to effectively prevent the acid from stimulating high water saturation sections. The field results show significant improvement on post stimulation production owing to effective diversion and water production control, compared with wells in which a conventional polymer diversion technique was used in the past with no consideration of high water cut cases. The new technique has been selected as the standard stimulation practice in most horizontal openhole carbonate wells in Kuwait. Introduction The Wafra field, discovered by Aminoil and Pacific Western (Inter Getty Oil) in 1954, is located in the Partitioned Neutral Zone - an area between the Kingdom of Saudi Arabia and Kuwait. The mineral rights in this region are shared equally between the two countries. The field is now operated by Saudi Arabian Texaco (SAT), a 100% owned subsidiary of Chevron, and Kuwait Gulf Oil Company (KGOC). SAT operates the field on behalf of the Kingdom of Saudi Arabia under the concession agreement signed in 1949. Out of the six reservoirs in the Wafra field, the most prolific is the Lower Cretaceous Ratawi Oolite. Production from this reservoir started in 1957 with 24°API being produced primarily under solution gas drive. By 1988, the average reservoir pressure had declined to 1,780 psi from initial reservoir pressure of 3,140 psi after production of almost 600 million bbl oil. Production curtailment was being considered as an alternative to reduce the pressure decline. The field was shut-in during the Gulf War and was then brought on-line shortly thereafter with extensive development drilling program. While the field was shut-in, the average reservoir increased to 2,302 psi, signaling the presence of a moderately active aquifer. The Ratawi Oolite formation permeability varies from 1 md to 1269 md and porosity ranges from 15% to 26%, with an average of 202 md and 21% respectively. The formation temperature is 150ºF. The current reservoir pressure of the main area has dropped to 1,800 psi, whereas the east-west area remains as high as 2,200 psi due to less development.

In an environment of high drilling activity and a limited amount of rigs, available alternative completion methods using Wireline or coiled tubing enables a more efficient drilling and completion process. For a successful completion, depth control is critical for the placement of perforating guns and completion hardware. Common practice is to perform the perforating using Wireline, which becomes challenging with wellbore angles over 60 deg. The use of coiled tubing enables the completion of highly deviated or horizontal wellbores, but depth critical operations performed using coiled tubing historically have presented industry challenges. Using the innovative real time depth measurement (RTDM) tool overcomes the limitations of other down hole depth-correlation methods. This paper describes the design, planning and execution of a completion in a horizontal well using coiled tubing and a RTDM tool. Introduction With high demands on the utilization of work over rigs to increase the available production levels; the improved use of resources and cost saving available by using coiled tubing to enable the execution of a sand control completion in a deviated well bore in the Gulf Coast of Mexico has lead some clients to optimize their operations with this technology. Completion Design There are a number of sand screen completions available on the market today from several service providers that can be run on coiled tubing in both mono-bore, or in through tubing1 applications. It is not within the scope of this paper to discuss the individual completion types, but more to cover the similar job design and execution principles that are required in all cases to achieve a successful operation. These principles are explored throughout this paper via a summary of a case history, however to list some main points, the following needs need to be considered as a minimum:–Rig Site Access–Available deck space and loading (crane limitations)–Personnel and equipment logistics–Simultaneous operations–Utilities and amenities–Well Bore Access and Preparation–Tubing Forces–Deployment/Well Control–Well geometry and construction–Well path–Reservoir and Completion–Production characteristics•Pressure•Volumes - solids, liquids and gases–Depth correlation–Ease of running and setting The completion design used, in the case discussed in this paper was specifically chosen for allowing the rig operation to be completed in the quickest possible time, leaving a secure well bore that could then be worked on with intervention technology to finalize the completion at the operators discretion. This allowed the required reservoir which was located in a small window of hydrocarbon bearing rock to be specifically located and produced, with the effect of any potential reservoir damage caused by the drilling process also being minimized or bypassed.