Throughout the last few years, oil company strategies have moved toward recovery of the maximum oil in place from mature fields and reservoirs that were previously considered technically challenging. The Mauddud formation in the Bahrah field is a low permeability carbonate formation with moderate to high oil viscosity. Viscosity is between 2 and 7 cp at 170°F, but a 90-cp viscosity at surface conditions is commonly observed once a well is placed on production, creating challenges for a vertically drilled well that could not provide necessary levels of sustainable production. In an attempt to achieve economic continuous production, a 3,000-ft lateral horizontal well was drilled. The lateral length was designed as an optimal solution for such a challenging reservoir to help sustain the production flow. Additionally, a multistage acid fracturing (MSAF) treatment was performed. This paper discusses the design, execution, and production of the first MSAF treatment performed in the Mauddud reservoir using a cased openhole completion with swell packers and sliding sleeves that were placed in seven stages across the 3,000-ft lateral interval. Post-operation analysis exhibited highly sustained production, creating a shift in oil company plans toward drilling new horizontal wells and applying MSAF treatments to move the Bahrah field into the development phase. Results obtained from this operation were effectively used to help improve production in similar mature formations. Based on this pilot treatment, a wide-scale field development strategy was planned, and many wells were drilled, completed, and fractured similarly in Bahrah field.
Proppant fracturing treatments in sandstone formations are routinely executed in Kuwait, however when carbonate formations are the target, acid fracturing is the preferred treatment method. It has been observed that acid fracturing delivers a high initial production however maintaining a sustainable production rate is a challenge in the tight cretaceous carbonate formations in Kuwait. A production enhancement technique needed to be identified in order to deliver more sustainable production and maximize recovery from these carbonate formations. The first stage of the project focused on ascertaining the operational feasibility of proppant fracturing in a single layered Mauddud reservoir. This paper will focus on the operational implementation of multi-stage proppant fracturing in the multi-layered Tuba reservoir. (Nagarkoti, M., et al., 2018) Based on global experience it was proposed that proppant fracturing can deliver more sustainable production rate as compared to acid fracturing. A predominant issue in previous acid fracturing treatments done in the Tuba reservoir has been fracture containment between layers. Proppant fracturing was also identified as a solution to mitigate this challenge. Proppant fracturing had been previously attempted in Kuwait, however the attempts were evaluated as not being operationally successful. The steps that lead to the recent first successfully executed proppant fracturing treatment in carbonates in Kuwait has been documented in Part I of this paper series. The cretaceous carbonate formations in North Kuwait are relatively shallow and are known to be tight and highly ductile. Due to the ductility of these formations, proppant placement and reduction of the fracture conductivity due proppant embedment were thought to be significant risks. During the course of the project, detailed core analysis and testing was conducted using formation core samples to ascertain the severity of this risk. Lessons learnt in the first stage of this project were implemented prior execution to ensure that the planned proppant fracturing treatment would meet or exceed operational expectations. Successful execution of this hydraulic fracturing treatment was pivotal in order to plan the future production strategies for the Tuba formation. A cautious approach needed to be followed as proppant placement was of paramount importance. Different strategies were incorporated in the fracturing workflow to ensure the success of the treatment and to maximize data collection in order to optimize future treatments and well placement. Multiple mini-fracs, temperature logs and pumping of novel non-radioactive tracer proppant were some of the techniques utilized. During execution various decisions were taken real-time to ensure success of the treatment. It was observed that all parameters were consistent with the results of the core and laboratory testing conducted during the initial phase of the project which lead to optimizing the proppant placement. The success of this treatment has been a game changer resulting in more wells being identified as candidates for proppant fracturing in this field. Once proppant placement was established in the first stage of this project, an attempt was made to optimize fracture designs, fluids and treatment schedules. The lessons from these optimizations will help further design implementations in the next phase of this project including fracturing of horizontal multi-stage wells which will help ascertain the future production enhancement strategy for this field.
Numerous methods have been applied in matrix acidizing over the previous decades to successfully stimulate multiple zones. These methods have also been implemented in fracture acidizing with varying degrees of success. This paper discusses the application of a new biodegradable material used for diversion in multiple zones or long formation intervals and presents improved results obtained using a new biodegradable diverter. Acid-fracturing diversion can be more challenging than diversion for matrix acidizing. To effectively stimulate multiple or large zones, the diversion treatment should be able to bridge not only the perforations themselves, but often inside the fracture system as well. This can be difficult because acid reacts with the rock, forming an etched/enlarged path, thus the diversion also requires bridging inside this conductive path. This differs from matrix acidizing techniques, in which the diversion depends mostly on the perforations in an interval(s) and the stimulated reservoir permeability. Historically, several methods have been implemented for acid-fracturing diversion, such as ball sealers, viscous fluids, packers, etc., resulting in limited success or cost-ineffective results. The new biodegradable material helps improve acid fracturing diversion success in multiple zones or long formation intervals. The development of this biodegradable material is discussed along with a case study. Also, details are provided of the biodegradable material evaluation that consists of 1) pre and post-temperature logs, 2) pre and post-injection logging profiles, 3) pre and post-production history, and 4) further recommendations. The results of the evaluation methods show that the biodegradable material can be used as an effective alternative diversion method to seal existing perforations and effectively stimulate all perforated intervals. Production increased more than threefold, and the targeted fracture height was achieved based on the temperature log data.
A few years ago, following an extensive field study in North Kuwait, several wells were sidetracked and converted as horizontal openhole water injectors to support reservoir pressures as part of a secondary recovery plan. Production improvement was immediate, but injection rates soon started to decline and injection pressures were rising, eventually jeopardizing oil recovery. Conventional acid stimulation only led to short-lived improvements, and more elaborate methodologies rapidly became uneconomical. A new stimulation strategy was needed. In these carbonate reservoirs, marked, sustainable improvements in injectivity can only be obtained through accurate placement of stimulation fluid across the entire interval, away from high-intake zones that develop as a consequence of repeated blind acidizing practices. A real-time, pump-through downhole flow measurement tool was used with coiled tubing (CT) to profile the openhole sections and identify thief and tight zones prior to treatment. The tool enabled adaptation of the stimulation strategy and was then used to ensure proper fluid placement during the pumping stages. Both profiling and pumping were performed in just one trip. This innovative tool and its cost-effective workflow unlock a new level of operational efficiency. Whereas previous approaches required mobilization of additional equipment, the proposed methodology allows profiling horizontal sections and treating them in a single run with the same bottomhole assembly (BHA). For the water injectors presented in this study, this represented a saving of 3 days of operations and the associated logistics costs as compared to using logging tools and tractors for profiling. Moreover, real-time downhole flow monitoring with CT opens new avenues for treatment optimization, and ultimately, stimulation effectiveness. It allows for a better control of fluid resources and placement while the treatment is in progress. Flow sensors can be used to obtain the initial injection profile in lieu of distributed temperature sensing (DTS), which typically requires long acquisition times in water injectors. In this study, the wells treated with this approach showed a sustained 100% increase in injection rate, with the injection pressure dropping to nearly 0 psi. The volume of stimulation fluid needed was also lower than expected, yielding additional cost savings. By providing direct, real-time downhole flow measurement, this new tool brings acid stimulation execution to a new level of effectiveness, an advance necessary to the sustainability of many production enhancement projects in Kuwait. Furthermore, the use of this new monitoring capability is more cost-effective than conventional stimulation approaches that have proven either inefficient or detrimental to wells in the long run.
Digital Slickline (DSL) Technology for production logging has been successfully implemented in South East Kuwait (SEK) oil fields. This advanced technology enabled Kuwait Oil Company (KOC) to save significant amount of deferred production and operational cost without compromising on the data quality. In addition, it reshaped how the operator performed surveillance operations through a more efficient workflow. A detailed analysis was carried out in more than 11 wells where production logging was acquired with DSL. Comparing the new workflow to the traditional workflow showed that DSL implementation saved around 51,000 barrels of deferred oil production and improved operational efficiency by 72% compared to the conventional workflow, without compromising on data quality during both real time and interpretation stages. Based on these results, KOC decided to implement this workflow in majority of the wells and now it has become the standard for production profiling in ESP wells.
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