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.
A recent study showed that Tuba reservoir, a limestone-rich formation, has the highest oil in-place of all upcoming reservoirs in North Kuwait. This tight formation has three main layers - Tuba Upper (TU), Tuba Middle (TM), and Tuba Lower (TL) with several reservoir units alternating with non-pay intervals. The reservoir units contain significant proven oil reserves; however, production performance after conventional acid fracturing treatments has been historically subpar. As part of new development plan, two horizontal wells, one in TU and one in TL were drilled to evaluate the production potential of a new completion strategy and technologies. This paper presents one such technology, a single-phase retarded acid system used as a pilot project study. In contrast with previous conventional emulsified acid systems, the single-phase retarded acid minimized tubing friction, thus enabling high pumping rates for the entire treatment. Alternating with the acid system, a viscoelastic surfactant-based leakoff control fluid system allowed the acid stages to reach deeper into the formation. To aid, degradable fiber technology was pumped in several stages to achieve near-wellbore diversion and further control leakoff into large natural fractures, thus improving the stimulated reservoir volume. These fibers are designed to completely degrade with time and temperature after the treatment. Delivery of the complex acid fracturing treatment was optimized in real time for each stage based on bottomhole pressure trend and response. Combining a new single-phase retarded acid system with chemical diversion technology has proved to be effective in maximizing lateral coverage and etched fracture half-length. Post-treatment evaluation of TU horizontal well revealed the initial production was as much as 150% higher than offset vertical wells after conventional treatments with gelled acid and as high as 100% higher than a previous multistage horizontal well treated with emulsified acid. The TL horizontal well was just put into production recently and is showing encouraging results considering the lower reservoir quality compared to TU formation. The success of this technique and technical combination delivered breakthrough results for this region and has engaged new interest in developing the Tuba reservoir.
With the goal of reducing non-productive time (NPT) and increasing operational efficiency, KOC decided to implement pilot projects to evaluate feasibility of intelligent digital oilfield (iDOF) concepts. The Kuwait integrated digital oil field in the Sabriyah field (KwIDF Sabriyah) pilot was implemented as a tool for real-time collaborative diagnosis and optimization of a water-flooded giant carbonate reservoir within the Sabriyah field. Initiated in 2011, KwIDF Sabriyah is currently extensively used for the monitoring and optimization of (a) waterflood, (b) electrical submersible pump (ESP), and (c) gas lift (GL) systems. KwIDF Sabriyah has increased the operational efficiency in many areas of daily engineering activities, including (a) reduction of excessive time spent on data acquisition and validation, (b) significant reduction of time on the identification of the root of failure of equipment, (c) collaborative decision-making with key stakeholders, (d) minimization of time between decision to execution by means of operations support services, and (e) prompt re-evaluation of optimization initiatives soon after implementation. This paper illustrates how the automated workflows are used by describing a typical working day at the KwIDF Sabriyah Collaboration Centre (CC) where the visualization of real-time well production parameters are provided to an integrated multidisciplinary team consisting of reservoir, production, process and well surveillance engineers. This environment supports the cooperative and proactive decisions never before achieved while functioning, not only in physically remote locations, but also in departmental silos within the company. An extensive case history is also provided to illustrate the new way work is being achieved and how it is adding value with ease, with the support of KwIDF Sabriyah workflows platform. The achieved results are reported in terms of sustained oil gain.
High reservoir heterogeneity and tightness necessitate the application of new stimulation technology targeting good fracture conductivity and deep penetration for effective productivity and recovery enhancement. With efforts of multidisciplinary team, new Acid Fracture fluid, diverter and high leak off control technologies have been designed and executed successfully as first time ever covering multiple layers in Mauddud carbonate reservoir in Bahra field. Mauddud is heterogeneous, tight multilayer limestone reservoir especially in Bahra field which is still under exploration phase despite having initial production early 1975. Owing to the low reservoir transmissibility, production performance has historically been poor, even with Artificial Lift and conventional Stimulation. Therefore, full-scale commercial exploitation of the Mauddud/Bahra reservoir requires advanced technologies for productivity enhancement. One of the oldest Mauddud vertical wells in Bahra field was drilled in 1974, completed across all Mauddud layers. It was initially produced naturally at very low rate and intermittent flow periods till ceased to flow in 2001. ESP was installed in 2007, and conventional Matrix Acid stimulation was performed with very steep post-treatment decline rate. It was produced intermittently for 4 months, and then closed in due to too low reservoir inflow. This well was selected for first application of Acid-Fracturing due to its relatively good reservoir development with high (~virgin) pressure, but low production rates. The job was designed to implement one-stage Acid Fracturing using new acid fluid diverter technology to enable covering all perforated Mauddud layers, and maximizing fracture conductivity and penetration. Many technical and operational challenges were faced and properly handled through integrated communication between different concerned teams with lessons learned are to be considered in next designs and executions. Post-Acid-Fracturing Production results showed initial high rate at high bottom-hole flowing pressure, followed by a gradual decline in rate and pressure representing transient flow period until reached reasonable stabilization. The nodal analysis has estimated post stimulation reservoir productivity improvement by ~3 folds based on the average stabilized rate and pressure. The positive results of this first Acid Fracturing has set up the foundation for productivity enhancement and Mauddud reservoir development strategy for existing and new planned wells in Bahra field. As a prompt action, 2 more wells (1 existing and 1 new) have been acid fractured with good results. It is expected that the oil gain potential will be significantly more in Horizontal Completions due to more extended reservoir coverage. Therefore, Acid Fracturing Stimulation for horizontal wells is under study for Bahra Mauddud Reservoir. The success of such application will formulate the drilling, completion and stimulation development strategy for the entire Mauddud Reservoir including early stimulation to improve initial productivity that will contribute significantly to the North Kuwait production target.
Openhole (OH) multistage fracturing (MSF) is increasingly used to stimulate and maximize production within low-permeability reservoirs in unconventional plays globally, extending its use from tight sands, shales, and carbonate reservoirs. Technological breakthroughs in hydraulic fracturing have helped enable OH MSF within lateral sections. The target reservoir is a tight heterogeneous carbonate with unsustainable productivity. The hydrocarbon produced is oil of relatively low API and gas/oil ratio (GOR). Given the challenging nature of the unconventional Mauddud reservoir of the Bahrah field, a sophisticated design of both the well completion and fracturing treatment is necessary to achieve the North Kuwait strategic production targets by maximizing reservoir contact and enhancingwell performance. A long horizontal well was drilled within the Mauddud reservoir. Completion technology was based on distributing swellable packers along the lateral section to develop MSF acidizing. The multistage packer and port designs were based on the reservoir mechanical and formation properties, to achievethe best fracture extension. Fracture acidizingwas performed on each stage, the well was flowed clean, and an electrical submersible pump (ESP) was run to produce the well. A production logging tool (PLT) survey was run immediately after fracture acidizing and six months after production. The recorded data indicated different contribution profiles of the stages, which indicated the fractures and production within such reservoirstake time to stabilize. This paper describes and addresses the effectiveness of MSF. Additionally, MSF performance in horizontal vs. vertical wells is assessed. Well performance analysis, exploitation approaches, and successful implementation are discussed, highlighting the advanced completion technology applied. The PLT results at different stages of the well life (post-acidizing and after ESP installation) are discussed. A comparison between the multifracture within the lateral section and vertical fractured well showed the benefit of the technology used to boost and sustain production. Effective horizontal drilling and MSF have helped enablethe development of unconventional resources, which were considered economically unfeasible previously.
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