The Barik formation is a low-permeability conventional tight-gas reservoir, in Block 61 in the Sultanate of Oman, comprised of a series of interbedded sandstone and mudstone (shale) layers. To achieve the most efficient and economic development of this formation sequence, the wells require the application of massive hydraulic fracturing. Such an approach was developed and deployed during the Appraisal stage of the programme and a considerable effort was placed in ensuring that the fracture height was contiguous, resulting in an effective drainage across all layers of the Barik formation. This approach was then encapsulated in the Full Field Development (FFD) planning Basis of Design (BoD) and was established as the approach to be taken throughout FFD. Until the field development was well underway, a single fracture treatment had proven sufficient to stimulate the entire Barik reservoir. However, as the development moved into the Southern area of the field, a substantial thickening of the Barik sequence was encountered and with this change successful complete vertical propped fracture coverage became much more challenging to achieve in an effective and repeatable manner. This paper demonstrates the approaches that were subsequently taken with the fracture design, the fracturing fluid selection and the fracture perforation strategy to address this issue and restore the achievement of complete fracture/formation coverage. Throughout the paper a number of examples will be presented that demonstrate the issues and effects that arose with the thickening of the Barik formation. The paper will then go on to examine how these effects were identified, what surveillance was used and the various characteristics that were displayed and how they were inferred. It will examine how the various issues were addressed, what changes were made to the fracturing strategy and demonstrate, through direct results, the outcomes that were subsequently achieved. This paper will focus on some of the principal issues that can arise when moving a developing fracture BoD in a laminated sequence into a more thickly developed environment with more extensive height and bulkier sands. The paper will provide a number of detailed examples of the issues themselves, and describe the detrimental and impactful effects that they may have on fracture coverage and hence well productivity and EUR. Additionally, the paper will describe the approaches that can be used in order to successfully address these effects. The paper will clearly demonstrate that when such considerations are taken into account that a successful suite of outcomes can be achieved.

Most of PDO's carbonate fields in North Oman have been producing for many years, initially on depletion in the early days but were quickly put on water injection to maintain reservoir pressure and safeguard long term ultimate recovery. As these fields mature into early middle age, EOR options have been under review to further increase recovery.Given the reservoir properties and the prevailing fluid & gas conditions for these carbonate fields, thermal technologies are not considered an optimal choice. Gas floods would potentially feature but were screened out due to the overall balance between gas requirements, cost and potential reward. Chemical floods with potentially attractive high recoveries were selected for further assessment.The goal is to demonstrate that chemical technology can produce economic incremental oil from a waterflooded carbonate reservoir containing a low-viscous light oil. The reservoir selected has undergone a successful waterflood implementation with good control on historical voidage and production allocation. The potential follow up chemical flood is then planned to be introduced in a phased manner. This starts with phase behaviour and core flow experiments in the lab to find a suitable chemical formulation to optimally mobilize waterflood residual oil. This is then followed by field trials such as a Single Well Chemical Field Test to back up lab experiments, extensive logging, a MicroPilot test and a planned potential multi-well pilot. Full field implementation is then dependant on the results of the earlier project phases and will have to balance against the perceived rewards, risk and cost. The results to date, learning's and key findings along with the selection strategy and challenges will be discussed in this paper. This study and field work will provide a foundation upon which the future potential for chemical flooding in North Oman carbonate fields can be evaluated and implemented.

Efficient multistage hydraulic fracturing in horizontal wells in tight-gas formations with multilayered and laminated reservoirs is a very challenging subject matter; due to formation structure, required well trajectory, and the ability to establish a conductive and permanent connection between all the layers. BP Oman had initiated the technical journey to deliver an effective horizontal well multistage frac design through learnings obtained during three key pilot horizontal wells. Since these initial wells, additional candidates have been drilled and stimulated, resulting in further advancement of the learning curve. Many aspects will be covered in this paper, that will describe how to facilitate the most effective hydraulic fracture placement and production performance, under these laminated conditions. These approaches will include the completion and perforation selection, fracture initiation zone selection, fracture height consideration, frac fluid type and design. The paper will go on to describe a range of different surveillance options, including clean-up and performance surveillance as well as number of other factors. The experiences that have been gained provide valuable insight and learning about how to approach a multistage fracturing horizontal well program in this kind of depositional environment. Additionally, how these lessons can potentially be subsequently adapted and applied to access resources in the more challenging and higher risk areas of the field. For example, this paper will present direct comparison of over and under-displaced stages; differences in execution and production for cased hole and open hole completions; and many other variables that always under discussion for hydraulic fracturing in horizontal wells. This paper describes in detail the results of many multistage fracturing trials by BP Oman in horizontal wells drilled in challenging multilayered and laminated tight-gas reservoirs. These findings may help to cut short learning curve in similar reservoirs in the Middle East Region and elsewhere.

This paper describes the journey of hydraulic fracturing design solutions and implementation in Khazzan field. More than 100 wells have been stimulated with hydraulic fracturing in the field in the last decade. Most of these wells were treated with a single-stage massive propped hydraulic fracturing treatment aimed at stimulating the entire vertical productive zone in a single treatment. More recently, hydraulic fracturing has begun on the southern acreage from Khazzan, referred to as Ghazeer. Producing layers in this area are thicker and higher permeability and, as a result, more prolific. Based on the available data and experiences, the establishment of clear guidelines has become a requirement to help the understanding and adjust the hydraulic fracturing design for each well to be become a well-specific optimum design. During the stimulation journey, surveillance techniques have been utilized and implemented in the Khazzan and Ghazeer fields to provide and develop better understanding of the fracture propagation process. These data have proven essential to support stimulation design evolvement and determine if multiple fracturing stages are justified or whether a single stage would be sufficient. Based on a wide range of hydraulic fracture stimulation operations performed across the Khazzan and Ghazeer fields, a flowchart was developed to integrate all the lessons learned from the previous experience and help optimize future fracture design. Clear guidelines include the rationale between the selection of single or multiple fracturing stages, the selection of optimal pad fractions, and other associated details of the fracture design. This flowchart has been extensively validated with surveillance and has proven its inherent value in many stimulated wells, with either single or multiple proppant fracturing stages.

It is well known that close quality assurance and quality control (QA/QC) are of vital importance for the successful placement of any hydraulic fracturing treatment. Many complex pieces of equipment and specialized personnel are involved in the fracturing process, and the following of strict QA/QC standards is mandatory to make these operations successful, efficient and safe. BP Oman is using massive hydraulic fracturing treatments to exploit the challenging tight-gas Barik Formation in the Khazzan and Ghazeer Fields. Each treatment is designed to place 1 million pounds of proppant into this tight, high pressure high temperature reservoir, leaving no space for error. Implementing QA/QC and logistic supply measures begins with the mobilization procedures: chemicals checklist/verification and mixing on the base, timely equipment maintenance, bulk plant proppant delivery to ensure a swift and smooth 24 hour operation. Water delivery management loading quality check, logistics, site acceptance and minimum quality checks are another important procedure related to this preparation. Each fracturing stage requires at least 14,000 bbl of fresh water to be available and quality checked on the site before the start of the fracturing treatments. Intensive QA/QC measures continue through the day of the fracturing treatment itself to ensure the equipment is in full working condition. Assurance that all of the supply systems are properly calibrated, all chemicals loaded and levels physically measured. During the fracture treatment itself all parameters are repeatedly measured and visualized in real time. Fluid viscosity is assessed on the fly and data verified with an HPHT viscosimeter also present on the wellsite. After the treatment, all remaining chemicals are measured once again and carefully assessed against the expected inventory values and material balanced. Implementing extensive QA/QC procedures enabled efficient mobilization between wells with mobilization time as low as 6 days despite the complex equipment and material needs for these massive fracturing treatments. Planned logistics and consistent quality checks before, during and after the treatment enabled BP Oman to successfully place more than 100 hydraulic fracturing stages with the amount of proppant exceeding 1 million pounds per stage. The bar has raised even higher with successful placement of 2 million pounds of proppant, the largest single stage hydraulic fracturing treatment in the Eastern hemisphere at the time of execution.