This paper presents a case study of a matrix acidizing treatment in a well located at the neutral zone between Kuwait and Saudi Arabia, whereby the combination of a "smart fluid" in a stimulation treatment pumped through a Coiled-Tubing (CT) with the real time distributed temperature sensing (DTS) technology helped improve the real-time decision process of fluid placement, temporary plugging placement, and treatment efficiency evaluation. As part of the analysis process and to facilitate the onsite decision-making process, a temperature inversion technique was also used to translate the actual temperature profiles into fluid invasion profiles across the horizontal open-hole section of the well. Additionally, a full scale acid placement and thermal modeling is proposed in order to perform an in-depth post-treatment evaluation. The bottom hole data evaluation further confirmed the benefits of using a smart fluid. Following the treatment, the well produced at a rate of 1500 bbl/day with 17% water cut, which is well below the field average of ~50%.
A limitation of Electrical Submersible Pumps (ESPs) is the inability to handle significant volumes of gas. The implications of this limitation become even more critical if the fluid production rate is at or below the minimum rate required for cooling of downhole equipment. The oldest and most widely practiced method for forced convection cooling of the motor of an ESP system is to use a motor shroud. However, numerous field case studies have shown that even with the motor shroud in place, motor failure has been the primary cause of ESP failure in low-volume high-GOR wells.The optimal mitigation solution for low-volume high GOR cased-hole producers is to lower the ESP string below the perforations, with a shroud installed for cooling of the motor. For low-volume high-GOR ESP-equipped producers that are producing from an open-hole interval installation of the same conventional shrouding system would take care of the cooling of the motor but it will not function as a free gas eliminating or reducing device. The production strings of the ESPs producing from an open-hole interval usually include an inverted shroud intended to reduce the amount of free gas entering the pump. Such installations would not function as a motor cooling device.The large degree of production loss and the increased operating cost incurred by unplanned ESP shut-down and failure have been two of the major challenges faced by the asset teams of South Fuwaris (SF) and Humma (HUM) Fields in PNZ-Kuwait, in their efforts to maximize the uptime of low-volume high-GOR ESP-equipped open-hole producers. A customized shrouding system was needed to simultaneously resolve the issues of motor cooling and the reduction of the amount of free gas entering the pump. The dual functioning nature of a shrouding system composed of a conventional shroud combined with an inverted shroud was the main feature that had to be incorporated in the design of such system.Through the continuous efforts of the South Fuwaris and Humma asset teams, a novel dual-shrouding system has recently been developed to fulfill the requirements of cooling of the motor and reduction of free gas entering the pump simultaneously. Multiple customized versions of this system have been installed in critical low-volume high-GOR openhole producers since the 4th quarter of 2009. Examination of historical operating conditions of ESP strings equipped with the new shrouding system showed a significant reduction in the number of ESP shut-downs due to underload, overload or high motor temperature trips, and a dramatic drop in the number of ESP failures caused by overheating of the motor.This paper discusses the benefits of the newly-designed shrouding system and its built-in perforated tail pipe, specifically designed for low-volume high-GOR producers in South Fuwaris and Humma Fields, and actual results achieved from field implementation of this system.
The South Fuwaris and Humma Fields are located in the Partitioned Zone between Kuwait and Saudi Arabia. The South Fuwaris Field commenced production in 1963, with the majority of its production from the Lower Cretaceous Ratawi Limestone/Oolite reservoir. The Humma Field was discovered in 1998, and has the only PZ production from the early Jurassic Marrat Formation. 95% of the wells in South Fuwaris and Humma produce via electrical submersible pumps (ESP).The remote location of both fields requires all ESP systems to be powered by individual diesel generator sets located close to the well heads. Based on the requirements of the preventive maintenance program for these generators, each generator set is scheduled for lube oil/filter change every two weeks, at which time production is shut-in. The shut-ins result in a considerable volume of deferred oil.A recent Root Cause Analysis study of the historical failures of the downhole production assemblies of ESP-equipped South Fuwaris and Humma producers revealed that a significant number of failures could be directly or indirectly attributed to the produced solids settling back into the ESP after shutdown. When the well is shut down, the fluid column above the ESP drains back into the wellbore through the pump, causing produced solids to be deposited in the ESP. This causes high current draw during start up and eventually leads to motor or cable failure, in many cases resulting in complete seizure of the ESP shaft.To avoid the production loss and ESP failures that result from well shut in, the asset management teams in South Fuwaris and Humma have developed a method for keeping wells on line while generator sets undergo lube oil/filter change.The purpose of this paper is to demonstrate how the downhole ESP is kept running while its power generator undergoes scheduled preventive maintenance work. The paper also demonstrates the in-field applicability of the generator set synchronization technique to the oilfield operations, and how this technique has maximized ESP run time in Humma and South Fuwaris Fields, saving Wafra Joint operations greater than $10 MM annually. As more new wells are being drilled and produced, the annual dollar savings increase even further, through the use of a simple and cost-effective process.
The Ratawi Formation is one of the well-known hydrocarbon bearing reservoir in many parts of the Middle East. South Fuwaris Field in Partitioned Zone between Kuwait and Saudi Arabia is one of the examples where Ratawi is the main pay. This reservoir has shown immense potential in-terms of production from different parts of this field. However, sharp water cut increase in some of the wells has challenged the existing understanding of heterogeneity distribution in the field. An integrated approach was applied to characterize the secondary porosity using the high resolution image logs, core data and open-hole logs. A workflow was developed to map the heterogeneity in the field and calibrate it with the available production data. The Ratawi Formation was deposited in a ramp, platform setting. It is broadly divided into an upper Ratawi Shale Member and a lower Ratawi Limestone & Ratawi Oolite Member. Major discoveries were made in the lower part of the Limestone Member and Ratawi Oolite at nearby Wafra Field in 1953. Since then, major efforts have been given to understand and map the complex porosity and permeability in the field in order to sustain the production. Though at places, presence of open fracture has been reported from the image logs, however multi-well study reveals no major impact of fractures on production. An innovative approach was implemented to extract the secondary or macro porosity formed due to leaching, using high resolution image data. Initially total porosity was estimated using high resolution borehole image log and subsequently a cut off was used to segregate the secondary porosity. The permeability was then derived from macro porosity using a complex transform. Core derived total porosity and permeability shows excellent match with the image log derived results. A geostatistical approach was applied through the static model building process to generate property maps using secondary porosity, effective porosity and derived permeability logs. A Clear degradation of reservoir property has been observed towards the NNW and SSE part of the field as it lies on the flank of the gentle anticlinal structure. Available production data validates the production rate is controlled by secondary porosity in Ratawi Oolite Formation. New wells drilled based on the property maps shows promising production results from Ratawi Oolite Formation. Single porosity geo modeling using the conventional open-hole logs has always been the first approach adopted by the industry. However, in mature carbonate reservoirs, well wise production always brings surprises. A novel approach was adopted to quantify the secondary porosity from the borehole image log which was further calibrated with the core data. Permeability was also calculated considering the secondary porosity as one of the key controller. Production data shows excellent match with the secondary porosity and permeability derived 2D maps; which has bolstered the confidence of releasing new well locations with better productivity.
Logging While Drilling (LWD) tools with natural radioactive sources present risks to drilling and field development teams, due to the safety hazards inherent to the use of natural radioactive sources in the tools. If any natural radioactive source is left in the hole due to drilling conditions, a complex procedure is required to abandon the hole and sidetrack it. Recently, a new sourceless LWD logging technique (NeoScope), which incorporates Pulsed Neutron Generators (PNG), was introduced to Wafra Joint Operations (JO). The new technique provides multiple measurements (Resistivity / Density / Neutron / Sigma / Spectroscopy) from a tool located in a single 26 feet long collar. The PNG* uses electrical power generated from the Measurement-While Drilling (MWD) turbine to generate a large cloud of fast neutrons. These fast neutrons interact with the formation atoms to generate formation hydrogen index, Sigma, and spectroscopy data. In addition, the fast neutron interactions generate a secondary gamma ray cloud that can be used to measure formation density (similar to standard density measurement). The first successful use of this tool in Wafra Joint Operations was in the first time for in South Fuwaris Field. The tool was run in a pilot hole with an inclination of 60°, cutting Ratawi Limestone and Ratawi Oolite reservoirs. The acquired data were excellent compared to conventional LWD data. The proven success of this new technology provides risk mitigation / elimination for future operations. Extra care should be taken when using natural radioactive sources while drilling. The use of Sourceless LWD technology is a good risk elimination. Proper planning is required to ensure tool availability (only available for 8 ½” hole)
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