All tight gas project appraisals are inherently dependent upon the ability to execute effective fracturing treatments; that allow the determination of sustainable production rates; and hence potential project economics. Unlike the North American tight gas business, where thousands of wellbores are drilled each year and operational infrastructure and service quality is proven and in place; the International gas market challenges are significantly different. Often, the key risk with international appraisal; is not the presence of the hydrocarbons themselves, but more likely a competent and efficient execution of the fracturing process; that is essential in order to maximize gas inflow performance required for optimum well productivity. The Khazzan-Makarem structures have substantial known hydrocarbon reserves; which to date have resisted an economic development. The unique reservoir challenges of these formations have been shown to require specialised operational, execution and technical expertise in order to be successfully appraised. The approach taken by the operator was to design the appraisal project with particular emphasis on the application of massive hydraulic fracturing treatments; as without successful stimulation, it was appreciated that the ability to evaluate well productivity and hence the development potential would remain elusive. The result of close cooperation between the operator and the service providers, included planning the stimulation strategy, the number/sequence of wells, well types, fracture design, development of a matrix and selection criteria for technology deployment as well as operational issues associated with individual treatment execution. A locally tailored and carefully planned workflow was developed, that addressed the fracturing design process, the impact on the service delivery and the overall performance of this extensive project. Information presented within this paper, will provide a complete understanding of the specific factors involved in tight gas stimulation (particularly in remote areas). Furthermore, it will demonstrate a methodical approach to the process of planning, execution, QA/QC and post treatment assessment.

One of the principle constraints to successful fracturing and stimulation, outside North America and a few select regions; remains the very poor QA/QC that is unfortunately the industry yardstick in low volume areas. This paper will describe a rigorous approach to the operational QA/QC which allows an operator to: provide assurance on the ability to effectively perform a treatment, maximise the opportunity for a successful intervention, ensure efficient delivery of data and minimise the overall costs. This paper will outline a suite of approaches which are both step-wise and encompass various operational stages such as contracting, pre-frac planning, frac operational execution and post-frac reconciliation. A number of the key considerations (in each of these areas) will be described in further detail, along with all of the necessary supporting tools, check-lists and recommendations as required.The paper will go on to describe examples of start-up operations which have actually benefitted from the application of this approach and will describe the potential pitfalls and outcomes which would have resulted, if the QA/QC regime had not been rigorously followed. Finally, the paper will describe the importance of the relationship which is developed, a priori as part of operational planning between the operator and the service company, and the impact that this can have on the outcome.The industry is littered with tight-gas exploration and appraisal programmes that have been aborted or curtailed, due to inadequate stimulation QA/QC and the poor results which they subsequently provide. All too readily, the formations themselves are held responsible for the lack of ability to stimulate and/or the poor subsequent production performance. Such poor performance is typically explained via the development of colourful and exotic theories and scenarios, which are formed solely in order to support such failure; rather than acknowledge the more commonplace actual cause(s) which lie directly with the operational performance of the service company and the operator themselves.

The Valhall field, operated by AkerBP, has been a major hub in the North Sea, on stream for thirty-eight years and recently passed one billion barrels of oil produced. The field requires stimulation for economical production. Mechanically strong formations are acid stimulated, while weaker formations require large tip-screenout design proppant fractures. Fracture deployment methods on Valhall have remained relatively unchanged since the nineties and are currently referred to as "conventional". Those consist in a sequence of placing a proppant frac, cleaning out the well with coiled tubing, opening a sleeve or shooting perforations, then coil pulling out of hole pumping the proppant frac. For the past few years, AkerBP and their service partners have worked on qualifying an adapted version of the annular coiled tubing fracturing practice for the offshore infrastructure - a first for the industry, which has been a strategic priority for the operator as it significantly reduces execution time and accelerates production. As with all technology trials, the implementation of this practice on Valhall had to begin on a learning curve through various forms of challenges. Whilst investigating the cause and frequency of premature screenouts during the initial implementation of annular fracturing, the team decided to challenge the conventional standards for fluid testing and quality control. Carefully engineered adjustments were made with regards to high shear testing conditions, temperature modelling, and mixing sequences, these did not only identify the root cause for the unexpected screenouts, but also helped create the current blueprint for engineering a robust fluid. Since the deployment of the redefined recipe, adjusted testing procedures and changes made to the stimulation vessel, there have not been any cases of fluid induced screenouts during the executions. The fewer types of additives now required for the recipe have lowered the cost of treatments and the lower gel loading leads to reduced damage in the fractures, thereby contributing to enhanced production over the lifetime of the wells. This paper describes the investigation, findings and the resulting changes made to the fluid formulation and quality control procedures to accommodate for high shear and dynamic wellbore temperature conditions. It discusses the rationale behind the "reality" testing model and, proves that significant value is created from investing time in thoroughly understanding fluid behaviour in the lab, prior to pumping it on large-scale capital-intensive operations. The study demonstrated that there is always value in innovating or challenging pre-conceived practices, and the learnings from this investigation significantly improved the track record for annular fracturing on Valhall, redefined fluid engineering for the North Sea and will inform future annular fracturing deployments on other offshore assets around the world.

The application of high viscosity friction reducers (HVFRs) in unconventional plays has steadily increased over the past years, not only as alternatives to conventional friction reducers (FRs) but also as a direct replacement for the use of guar-based fluids. HVFRs demonstrate more efficient proppant transport, due to their unique rheological properties, concurrently with a high friction reduction effect allowing higher pumping rates. However, all these benefits come with few critical limitations related to frac water quality, compatibility with other additives, and static proppant suspension, which makes them very similar to conventional crosslinked gels regarding their Quality Assurance and Quality Control (QAQC) requirements at a well location during the field implementation. This paper illustrates the comprehensive laboratory efforts undertaken to evaluate different HVFR and crosslinked gel products, their successful field application supported by a robust and effective field QAQC process, and the critical importance of maintaining effective field-laboratory-field interaction/cycle to optimize the fluid design and maximize the results. Experimental studies on different products were conducted to measure the effect of frac water quality, HVFR loading, breaker loading, and compatibility with other additives used in the fluid recipe such as surfactants, scale inhibitors, and biocides. The ability of HVFR to suspend and transport proppant is not only a function of polymer loading but also highly influenced by fluid velocity as static and semi-dynamic proppant suspension tests demonstrate. Additionally, a full dynamic proppant transport test was also conducted using a multi-branched slot apparatus to simulate the flow inside a complex fracture network. Field execution followed a strict QAQC protocol including water analysis, field laboratory tests, water filtration, mixing procedure, product storage, and transport allowing direct onsite replication of the results that had been previously obtained in the laboratory. Constant communication between the field and the laboratory allowed a successful execution of several treatments in a challenging shale play in the Sichuan Region, China. These treatments achieved record proppant placements and, just as importantly, they demonstrated repeatability and consistency over time; which had not previously been attained. Laboratory testing proved critical in confirming that product segregation was occurring, even if there was no visual observation of this phenomenon, which had resulted in initial difficulties in fluid quality and reliability. The presence of constant QAQC engineering support on location was instrumental in rapidly identifying the potential root cause(s) and efficiently and correctly applying the necessary corrective actions. This paper will highlight the importance of laboratory testing, in order to design and optimize the fluid system. The paper will also demonstrate how critical the onsite QAQC is through actual examples of fluid optimization and field implementation. These two activities, although requiring a substantial resource commitment and effort, are both required to achieve successful execution.