Proppant Surface Treatment and Well Stimulation for Tight Oil and Shale Gas Development
Production from shale gas and tight oil resources has surged in North America due to new hydraulic fracturing technologies and its development has profound implications for Canada. For example, in Alberta, light oil production has increased due to contributions from tight zones in formations such as the Cardium and Viking and more growth could take place if the Duvernay and Montney formations are developed. In Saskatchewan, tight oil production from the Bakken formation has been significant. However, the environmental and economic sustainability of hydraulic fracturing has been in question, particularly with respect to the rate of recovery, the rate of production decline and high costs.
During hydraulic fracturing, a “fracking fluid” (consisting of water, proppants and additives) is pumped into the wellbore at a high rate and at a pressure high enough to cause the reservoir rock to fracture. The resulting cracks enhance the flow of oil and/or gas to the wellbore, and are kept open by the proppant (typically sand) after the removal of hydraulic pressure. Proppant Surface Treatment (PST) and Well Stimulation (WS) technologies are fracturing techniques that have the potential to increase the efficiency of oil and/or gas extraction. To that end, Petroleum Technology Alliance Canada (PTAC) led the submission of a proposed project Proppant Surface Treatment and Well Stimulation for Tight Oil and Shale Gas Development for ecoEII funding. The Project was awarded $217K from ecoEII.
PST and WS technologies are based on a chemical treatment for sand and ceramics developed by 3M Canada. The treatments are designed to alter the wettability of a surface to neutral wet. In PST, ordinary sand proppant is replaced by chemically treated sand. PST reduces surface tension on sand particles, allowing liquids such as oil, condensate and water to flow more easily. In WS, the wellbore and the fractures themselves are treated in a remedial operation applied to an existing liquids-blocked well. WS reduces capillary pressure reduces capillary pressure and increases the mobility of liquids, thereby increasing the relative permeability of gas, condensate and liquids and increasing production.
During a workover in October 2015, a well in the Alberta Cardium formation was pre-flushed with a solvent and treated using 3M’s WS-1200 chemical technology. The well was then placed back on production and after an adjustment period, stable production resulted. Six months later, the pilot well’s gas production returned to what it was before the workover, with an increase in condensate to gas ratio. The increase most likely indicates that the chemical treatment performed as intended. However, it is possible that the solvent wash contributed to the increase.
In 2012-13, a senior oil and gas company tested the PST technology in three vertical wells and one horizontal well for the purpose of determining if the new technology would lead to improved production over time. Three years of production data from these wells provided the opportunity to analyse the effectiveness of the PST technology using advanced reservoir engineering methodologies. Rate Transient Analysis (RTA) and Pressure Transient Analysis (PTA) was performed to determine if production forecast would show better expected ultimate recoveries for treated wells than untreated wells. Results indicate higher condensate productivity. However, the vertical wells appear to have suffered operational difficulties unrelated to the technology that, in some cases, overwhelmed the benefits of the technology.
Benefits to Canada
The Project demonstrated that the WS and PST technologies can be implemented by existing service companies and operators in Western Canada, and higher condensate production could be beneficial to future operations.
The trials analysed during the project will continue to be monitored. Durability of the chemical treatment should be validated in order to firmly establish the value of the condensate production increases. Moreover, all aspects of the implementation methodology should be reviewed and potential efficiency improvements and cost reductions identified.
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