Excess fluid leak-off, a challenge in Kuwait's naturally fractured tight carbonate formations, can compromise post-fracture productivity. Past acid fracture treatments, both for moderate and high temperature formations failed to generate the long differently etched fracture due to excessive leak-off. Treating zones with multiple perforated intervals in a single stage, particularly in pay zones with long heterogeneous rock properties can result in non optimal stimulation. Therefore, a new approach was developed with proven success to enhance fracture conductivity and overall production by efficient control of fluid leak-off. This novel approach incorporates the use of far-field and near-wellbore diverting systems into the acid fracture design. These solid particulate diverters (SPD) include low and high temperature systems that provide enhanced near-wellbore diversion in both case and open-hole applications. The SPD are designed to bridge across perforations and fractures in the higher permeability zones, diverting the stimulation fluid into lower permeability zones. A smaller sized multi-modal distribution of SPD controls the fluid in narrower natural fractures and wormholes, deepening penetration of the stimulation fluid along the entire fracture length. The SPD agents are fully degradable and do not contribute to permeability loss of the created fracture or the perforated interval when production starts. The production of the wells where the SPD agents were applied were higher in comparison to expected production of offset wells where non-acid crosslinked fracturing pad stages alternated with gelled or emulsified acid, and visco-elastic surfactant (VES) slugs. Both crosslinked fracturing pads, VES and emulsified acid slugs do not effectly control live acid leak off. Two case histories, documenting successes where this new approach to acid fracturing has been applied in the Tuba and Middle Marrat formations, have superior production results that correspond to enhanced fracture geometry.

In the early days of the oilfield, matrix acidizing was considered useful only for stimulating carbonate formations. However it has been known for many years that with proper job design, acid and additive choices, and in-depth study of potential formation damage sources, matrix acidizing can safely and successfully stimulate production in sandstone formations. By incorporating carefully designed tubing pickle, pre-flush, main acid system and post-flush (including optimum doses of corrosion inhibitors, mutual solvents, iron control agents, clay control additives, surfactants, etc.), matrix acidizing can provide excellent productivity improvements even in sandstone formations with complex mineralogy. This paper describes a matrix acidizing campaign executed successfully in the Gulf of Cambay (Khambhat) on the west coast of India. In initial laboratory tests and during simulation runs, it was aimed to design a pre-flush, acid system and post-flush to best suit the challenging reservoir conditions while also considering offshore logistics. Further as the formation had iron-rich minerals like chlorite clay, siderite, etc., a chemically modified organic sandstone acid system was selected as opposed to conventional hydrofluoric acid system. Moreover a spacer system was designed and pumped to push any iron precipitation far away from the near-wellbore area and to clean the area for the organic acid system. After pumping the system in one well, the system design, pumping procedures and volumes were modified to further improve results in the next well. Fines-stabilizing agents were introduced to avoid clay migration or swelling that may otherwise jeopardize a successful treatment. The paper will explain the basis for modifying the design and pumping procedure, based on lessons learned from the prior operation.

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. Based on global experience it was proposed that proppant fracturing can deliver more sustainable production rate as compared to acid fracturing. Proppant fracturing had been previously attempted on two occasions in Kuwait, however both the attempts were evaluated as not being operationally successful. Hence prior to executing the first successful proppant fracturing treatment in carbonates in Kuwait a thorough study was undertaken to identify and mitigate the possible risks. 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. Successful execution of this hydraulic fracturing treatment was pivotal in order to plan the future production strategies from these formations. 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. Now that proppant placement has been established the objective of future treatments is to optimize fracture designs, fluids and treatment schedules which will help the future production enhancement strategy for this field. Lessons learnt from this first successful well will be applied to future wells planned in carbonate reservoirs in Kuwait, in order to maximize recovery.

The proposal of this paper is to share the case history and knowledge learned in this first application of the multistage zipper frac procedure and techniques in Biogenic wells. This breakthrough achievement was planned and executed by ADNOC Onshore Biogenic Drilling Department in Abu Dhabi which involves seven different services, each has a high importance and close collaboration was a key contributor to the feasibility of the project and the collective success obtained. The Zipper frac method selected and tailored by the Biogenic Team for the specific application enables to significantly increase the number of fracs per day performed over 2 wells. This technique stages multi-well completions, where wells are completed in a back-and-forth manner. One well is being pumped /fractured while the other well is being plugged and perforated for next stage. One of the key achievements in the Biogenic Zipper frac operation lies in the easy switch from line to another by using a manifold in a safe manner and without confusion. Because of the focus and high potential of Biogenic gas, Biogenic Team faced the challenge of delivering the two wells on a very tight schedule. This led the Team to review, select and implement a novel methodology that would deliver time and cost savings to the Project. New ideas were scouted and analyzed by different departments and service companies to select the most appropriate. Upon selection of the zipper frac method, meetings were done to issue and finalize a proper implementation plan for this multi-frac operation, which was a first in ADNOC Onshore. Explaining in workshops to key stakeholders and respective higher management the methodology and plan as well as the associated savings was essential to get full support and endorsement for implementing this method. There was no doubt that this method was the best way to achieve the goal with the tight given timeframe. Successful implementation resulted in of around 50 days savings compared with applying the conventional multiple frac procedure / method on a well-by-well basis. Wider application of this method represents a breakthrough in delivering future fracked wells cheaper and faster thereby bringing significant savings to future Biogenic gas development projects. Because of the importance of ongoing assessment and potential future development of Biogenic gas and unconventional resources, sharing details of ADNOC Onshore first implementation of the Zipper frac methodology is of benefit to the industry. The detailed account of its implementation (inclusive of added important technical features such as dissolvable plug and perf technology) that has delivered safely and successfully twenty-four (24) staged fracs in a short time frame represents a piece of useful knowledge.

Water dump flood is a non-conventional and cheaper alternative as compared to surface water injection commonly used to support reservoir pressure. The major costs associated with surface injection includes water treatment as well as sourcing of the water. The dump flood technique helps eliminate these costs thereby improving project and field economics. A dump flood technique eliminates the requirement of drilling an additional water producer well. In order for the dump flood technique to be successful, adequate production from the source and good injection rates into the target interval are key requirements. If either one of them are not met there is likely to be detrimental effects on the objective of the dumpflood. This paper details the risks and challenges identified for the subject well and the methods & technologies implemented to ensure the success of the project. As part of the water injection strategy in the subject field, water dump flood was deployed. These wells source water from a prolific aquifer and with the aid of artificial lift, and the water was then injected into the upper reservoir to improve sweep efficiency and pressure maintenance. Dump flood technology uses two perforation intervals : one source interval and another as an injection interval. For the subject well, water productivity was established from the source formation. Upon initial tests, the target injection zone showed poor injectivity both pre- and post- matrix stimulation. Hence a new strategy of implementing hydraulic fracturing to improve the injectivity in conjunction with the dump flooding technique in the subject well was attempted for the first time in Kuwait. Special consideration had to be taken while optimizing hydraulic fracturing design taking into account pump discharge pressure and formation closure pressure. This paper also covers the special design considerations taken into account when selecting and designing the artificial lift equipment for a fractured and dump flooded well. Successful execution of hydraulic fracturing was critical in order to achieve the required injectivity in the target formation. During the execution of hydraulic fracturing, it was observed that once the near well bore damage was by-passed, the fluid leak-off increased significantly due to high formation permeability. This paper will detail the various decisions taken during operational execution to ensure success of the treatment. Post fracturing results that contributed to the success of the first hydraulically fractured dump flood well in the country will be discussed. This success ensured that the well could be completed with the designed completion and artificial lift strategy resulting in minimal workover requirement. The lessons learnt from this first hydraulic fractured dump flood well will be applied across the field. The technique will help to optimize recovery and project economics through efficient injection. This technique unlocks a new method which will play a significant role in maximizing oil recovery in Kuwait.