A comprehensive diagnostic data-fracturing campaign (Fracture Pressure Analysis: FPA) was undertaken by the Gas Fields Development Group (GFDG) of North Kuwait in January-March 2013. The campaign involved executing FPAs on the primary zone of interest (Organic-rich Carbonaceous Shale: OCS) as well as underlying and overlying carbonates to establish "fraccability" and in particular the hydraulic frac vertical containment aspect, which are much needed for the successful planning of an appraisal program. This paper summarizes the resuts of those FPA tests and how the acquired data is used to calibrate the wellbore geomechanical model. This initial FPA campaign is the onset of a more comprehensive evaluation program planned for 2013 onwards. FPA sequences were executed on the OCS, underlying and overlying formations with encouraging results. The main concern was whether the OCS would yield hydraulic fracture (fracture initiation) below surface treatment pressure limitation of 13,500 psi (Maximum allowable surface pressure). The fracture initiation was successfully established in all three zones. In addition, multiple "fracture re-opening tests" were performed to evaluate the ranges of the fracture closure stresses during the leak-off. Multiple down-hole memory gauges were utilized to ensure elimination of wellbore effects on treatment pressure. KCl-laden incompressible water-based fluid system enhanced with friction reducer was utilized in all three stages to ensure minimal friction loss and damage. This formation suite has very complex mineralogical attributes as it is a mixture of clastics, carbonates and hydrocarbons, with reservoirs that can be very tight (possibly at micro-Darcy). This campaign will lead to an optimal selection among the vertical completion options (hydro-fracturing design), and will help to successfully plan for horizontal well completions.
North Kuwait Jurassic Gas asset development has strategic value of gas independency for Kuwait as it is the only non-associated gas producing asset. This paper will share the experience, added value, challenges and lessons learned from the successful implementation of first ever Hybrid 15k Multi-Stage Completion in Kuwait across Najma unconventional gas carbonate reservoir commingled with lower cemented liner completion in conventional Middle-Marrat tight carbonate reservoir. This completion configuration enables acceleration of selective stimulation and testing of Najma unconventional production potential in existing wells, and simultaneous comingled production from both reservoirs to maximize well production potential. The development of North Kuwait Jurassic deep unconventional gas carbonate reservoirs is key to compensate the production decline from conventional producing Middle-Marrat reservoir and to achieve the production target of Jurassic gas asset. The recovery from such unconventional reservoirs is extremely challenging if conventional development strategies are applied. Therefore, a dedicated full development plan applying integrated upstream and downstream technologies is important to achieve commercial production. The NK field development team has initiated a study to test the potential of unconventional Najmah formation in existing wells to evaluate the production potential and accelerate production from such reservoirs. The typical completion of Jurassic wells include Najmah reservoir in the 7-5/8″ cemented liner section followed by the Marrat reservoir completed in 5″ or 4.5″ cemented liner section. The multidisciplinary team efforts have yielded an innovative hybrid completion solution of 15K rated cased-hole ball-drop multistage completion across Najma reservoir layers and cemented liner across Middle-Marrat reservoir layers that allows selective commingled production of Middle-Marrat and Najmah with ensuring full selective stimulation potential across Najmah reservoirs through the multistage completion. Many completion design, operations and installation challenges were resolved to ensure mechanical isolation of lower depleted conventional reservoir before perforation the upper unconventional reservoir and running the multistage across it. This is to mitigate the challenges of high differential pressure of approximately 5,000 psi between the two reservoirs in completion phase to avoid high formation damage to the depleted Middle-Marrat lower reservoir plus well control during rig operation. This innovative hybrid completion has been installed successfully in one well as first time ever in Kuwait. Najmah and Middle Marrat reservoirs have been selectively stimulated and tested individually then commingled production from both reservoir as first time in Jurassic gas fields and Kuwait. PLT showed positive production contribution from Najma open frac ports and no cross flow among open reservoirs. There is a plan to expand such Hybrid completion to other candidates. This innovative completion configuration can be used in similar application for commingling production to minimize cost of new wells for different reservoirs.
Deep, unconventional tight carbonate reservoirs in northern part of the Middle-East present many challenges for field development. These challenges are due to the inherent very low porosity characteristics with an average 2 to 6% matrix porosity and 0.01 to 1.5 mD permeability. Natural fractures play a primary role in the producibility of these reservoirs. High angle well is being planned as a way to intersect as many fracture systems as possible for production improvement. To better visualize the subsurface structure while drilling, Ultra Deep reservoir mapping while drilling was deployed to map the whole reservoir boundaries in real time and know the formation dip and precise trajectory position from reservoir roof and base at any point in the lateral section. The 3D reservoir mapping gives precise geological geometry of the reservoir and enhances the placement of the well. The information from Reservoir Mapping While Drilling integrated to other downhole measurements such as Near bit Gamma Ray, Resistivity and the surface logging of gas composition and geo-chemical data could help immensely to determine the productive fracture zones. The foremost drilling challenge in deep Jurassic carbonates is exposure to high borehole temperature which can go up to 300 degF, due to high friction factor at depths of more than 12000 ft vertical depth from sub-sea (TVDSS), combined with high temperature gradient. This downhole high temperature environment almost reaching LWD tools maximum temperature thresholds, could potentially affect the LWD tools while drilling because of excessive fatigue to the electronics. This paper will discuss the case study of well placement challenges in deep Jurassic tight carbonate reservoirs and solutions to ensure of the success of the well operation and achieve well objectives.
North Kuwait Jurassic Gas asset has strategic importance for Kuwait production strategy as the only non-associated gas producing fields in Kuwait. This paper demonstrates the added value, experience, challenges and lessons learned of recent paradigm shift in Jurassic tight gas wells’ completion strategy from cemented liner to multistage completion. A successful expansion of Multi-Stage Completion (MSC) technology has been achieved on field level led by integrated team efforts since early 2020 to date. This helps to enhance overall well production potential, selective stimulation, overcome reservoir and intervention operations challenges, and early production delivery. The Jurassic gas asset produces mainly from deep high pressure and temperature, conventional and unconventional tight carbonate reservoirs. The recovery from such complex heterogeneous reservoirs is extremely challenging if conventional development strategies are applied. Due to the high reservoir tightness, permeability contrast among different flow units and dual permeability effect (matrix and natural fractures), well productivity potential significantly depends on the effectiveness of subsequent stimulation treatments of such complex heterogeneous reservoir to improve well productivity and connect the natural fractures. Selecting proper well completion is critical to overcome such reservoir challenges and ensure efficient acid stimulation treatments of such unconventional formations that need convenient diversion mechanism during the stimulation to enhance the productivity of each individual reservoir layer, and enable future flexibility of selective re-stimulation and reservoir management. The asset team has applied a step change in completion strategy to open-hole HPHT multistage drop-ball completions using state-of-the-art MSC technologies including closable frac ports, full 3.5in monobore post milling and debris sub to protect the MSC string during upper completion operations. This is to overcome such reservoir complexity, eliminate wellbore cleaning and multiple perforation intervention operations challenges and risks, eliminate cement quality uncertainties, improve overall cost, and fast track well delivery to production to meet asset production target by significantly reducing operation time from approximately one month of plug and perf technique to less than one week of continuous and less subsurface intervention operations. Total of 23 new Multi-stage completions were successfully installed in last 2 years including 4 systems in horizontal unconventional Najmah reservoir with overall good production results and significant improvement in selective acid stimulation (matrix and Fracturing), intervention operations efficiency and fast well delivery to production. Therefore, the asset plans to continue expansion in Multi-stage completion strategy. Based on gained experience, an integrated protocol for multi-stage candidate well selection, staging design and installation procedures workflow has been built by the integrated multidisciplinary team to ensure standard process across fields which can be used for application in other fields.
Currently, Kuwait Oil Company (KOC) is successfully producing from high pressure and high temperature formations. The reservoirs are deep with True Vertical Depth (TVD) approximating 15,000 feet, and pressures and temperatures of 11,000 psi and 275 o F respectively. The formations are composed of carbonates both tight and porous. The produced hydrocarbons are of high H2S and CO2 content, up to 10% and 12%, respectively.The aforementioned sour environment in addition to water cut occurrence during the production phase have led to scale creation. In addition, corrosion, erosion and pitting also occur, requiring well intervention to sustain production. Furthermore, well monitoring is essential and planning for workover and well interventions is becoming unconventional with higher associated risk.The recent scale removal activities proved to be very challenging with weight loss seen from the coiled tubing (CT) of approximately 7,000 Ib and CT leakage while operating at the hole condition. The CT pressure control equipment failed due to sudden increased in H2S concentration, which was attributed to the chemical reaction between the cleaning fluid (15% HCl) and the well fluids/scale mixture. This paper explains the well history, objectives of operation, execution history, procedures and causes of these challenges. Hence, lessons learned, observations and knowledge gained by the Kuwait Oil Company (KOC) are evolving, advancing, and being employed at an accelerated rate despite high cost.
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