Operational QA/QC: What You See is Not Necessarily What You Get
Abstract: 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 pap… Show more
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Cited by 5 publications
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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.
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.
8070 Miles from the Field to the Lab and Back: A Pragmatic Sequencing of Laboratory and Field-Based Fluid Testing and QAQC, A Case History from Sichuan Region, China
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.
An optimist says the glass is half-full, a pessimist half-empty, whereas a good engineer says that the glass is twice as big as it needs to be. There has been much debate over the years about the relative functionality, application and even necessity of proppant in delivering effective hydraulic fractures. Often these debates have been directly linked to major changes in core frac applications, more recently in the dominant North American onshore unconventional market. However, the debates have all too often used broad or unclear brush strokes to describe shifting fracture requirements. Meanwhile, the developing oilfield in the rest of the world resides in more permeable areas of the resource triangle, great care must be taken to ensure that conventional lessons hard learned are not lost, but also that unconventional understanding develops. Over recent years there have been many debates and publications on the relative value of the use of proppant (and associated conductivity), although the true question was about appropriate fracture design in different rock/matrix qualities and environments. Certainly, the vast majority of fracturing engineers appreciate the difference between continuous proppant-pack conductivity and other techniques, such as infinite conductivity, pillar fracturing or duning designs. However, there is increasing evidence that conventional fracturing is suffering from populist attitudes, leading to ineffective fracturing. Additionally, and just as impactful, that unconventional fracturing continues to rely on the lessons learned and physics derived directly from our conventional experience but applying this in an entirely different environment. Primarily, the main concern is with the transfer of recent lessons learned and techniques utilised in one rock quality and environment, to an entirely different scenario, resulting in the misapplication, reduced IP30, poorer NPV or reduced long term EUR and IRR. Examples will be referenced where appropriate proppant selection and frac design can be the difference between success and failure. Fundamentally, we have not sufficiently developed our understanding of the role of proppant and conductivity, for application in unconventionals and thereby rely far too much on our previous conventional thinking. While at the same time we are exporting often inappropriate unconventional populist practice into very conventional environments, thereby potentially achieving the abhorrence of the worst of both worlds. This paper will describe and address scenarios where appropriate engineering selection, rather than popularity-based decision making, has resulted in a successful outcome. It will also attempt to ensure that we show the importance of studying your rock, in anticipation of engineering design, and that this should be a key consideration. The paper will also suggest that as an industry we urgently need to address our approach to consideration of conductivity, placement and importance and ensure that unconventional knowledge and learning progresses with a beneficial outcome for all.
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