The Viking formation in southern Saskatchewan Canada represents an active area where steep production declines in the first year of production are common and are often attributed to wellbore or near-wellbore precipitation of paraffin. Excessive decline rates within the first year on production have been observed.A producer was experiencing paraffin deposition in the wellbore and suspected it to be the reason for production declines. Conventional treatments targeted at wellbore deposition were carried out with little effect on production rates. In an effort to improve production rates horizontal treatments were attempted. These treatments resulted in brief increases in production (up to 6 weeks). Horizontal treatment success led to investigation into other treatment options. Precipitation in the formation may contribute to reduced conductivity and, therefore, lower oil production rates. Solid paraffin inhibitors delivered via hydraulic fracturing offered the best potential for success in new wells.The chemical additive treatment was designed through product selection testing using cold finger deposition tests, compatibility testing with the hydraulic fracturing fluid system, and proppant crush prediction models. A baseline of the untreated oil characteristics was determined using offset wells. Pour point, carbon number distribution and wax percentage were analyzed in offset untreated wells and each treated well. Production trends were used to track the performance of the treatments. The solid inhibitor application effectively prevented conductivity restrictions due to paraffin precipitation issues in the proppant pack.Placement of solid paraffin inhibitors into the Viking formation with the proppant during hydraulic fracturing increased cumulative production by approximately forty percent in the first 350 days on production and reduced decline rates. Comparing 150 untreated wells with the 90 wells treated with the solid paraffin inhibitor in 2012 has increased revenue by about 15.8 million USD over the 350-day period. Wells drilled in the same area, with similar frac treatments, depths, horizontal lengths and stages were compared.
Experience has shown that hydraulic fracturing operations can introduce and/or stimulate microbial populations in the wellbore that in turn may lead to undesired corrosion, souring or other production issues. Biocides are applied to prevent the establishment of problematic microbes. Characterizing and quantifying which microbes will be introduced to a well using molecular techniques allows for optimized or even proactive treatment and prevention strategies to be implemented, whereas, traditional microbial testing methods have proven insufficient. Once the standard for microbial assessments in the oil and gas industry, culture media bottles are now just one of many available tests. Tests vary by their resolution (culturable, active and living, total microbes), and the information they yield. Some tests target very specific microbial subgroups of concern (culture media, qPCR), while others evaluate all microbes within the sample (ATP, qPCR, 16S rRNA sequencing). In the case studies presented, water and produced fluids were collected from all pertinent frac sample points (source waters, pre- and post-chem and post completions) and were assessed using the suite of microbial methods stated above. Three case studies are presented with several noteworthy observations regarding the value microbial tests provide to frac operations. First, culture media-based testing consistently resulted in incoherent and confusing data that failed to correlate with the remaining testing technologies. Second, ATP technology provided efficient and timely testing which lent itself well to on-site, evidence-based decision making. During one of the fracs, ATP results were used to modify and optimize a microbial control program on-the-fly. Third, DNA-based testing (qPCR and 16S rRNA sequencing) provided the most comprehensive insight into the microbial communities exposed to the well, and those that established post-completions. Overall, holistic microbial testing offers the user key information required to design and implement successful microbial control programs for frac. Without it, microbial issues plagued production efforts. Culture media tests provided limited and unreliable information and were deemed not suitable for frac operations. ATP provided a useful microbial load in real-time but could not elucidate the types of microbes present. DNA testing filled this gap by providing quantities and types of microbes present. Apart from assessing microbial control programs during the frac, monitoring the production fluids is essential to assuring continued well performance. The acknowledgment of the role microbes play in well completions, and the testing technology to evaluate oilfield microbes is rapidly advancing. Here we present some of the first case studies highlighting the use of molecular, DNA-based technology for assessing hydraulic fracturing operations and showing the fallacy of culture media-based testing which is the current industry standard.
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