Fracturing in Challenging Low-Temperature Reservoirs: Combining Laboratory and Field Approach Produces Promising Results

Abstract Development of traditional oil reservoirs is becoming increasingly challenging with time as more reservoirs move to brown state. The Bashkiria field complex is typical example of such reservoir: development started in 1932 and as of today, more than 80% of initial oil reserves have been produced. Thus, the only method to make wells produce economically is hydraulic fracturing. Particularities of the region are viscous crude oils, small net height of the reservoir, and low bottomhole static temperatures coupled with depleted reservoir pressure. This imposes additional constraints on the hydraulic fracturing design. The typical practice in region is to employ an aggressive pumping strategy to maximize fracture conductivity and minimize the amount of fluid pumped into the reservoir. Robust fluid is required to avoid premature screenout due to proppant settling. Another essential component of the fracture conductivity is fracturing fluid breakers. The goal in using breakers is to reduce fluid viscosity and break polymer residues in the proppant pack after treatment to facilitate fracture cleanup. Traditionally, breakers based on ammonium persulfate (APS) (both live and encapsulated) are used in Russian oil fields. They have proved successful in the typical conditions of Western Siberia (80 to 120°C). Enzyme-based breakers have limitations on temperature range and fluid viscosity range. In this paper, we focus on development of novel fracturing fluid tailored for Bashkiria oilfield conditions. An enzyme breaker was compared with traditional oxidative breakers. Production analyses were performed using actual treatment data and post-fracturing production data and comparing them with conventional treatment results. Laboratory testing proved that in terms of fracture-pack conductivity, the new enzyme breaker produced approximately twice the conductivity, as did oxidative breakers over the temperature range of the Bashkiria region. Implementation of novel fluid with pressure-independent viscosity behavior led to a reduction of more than twice the screenout rate with zero fluid-related screen outs. Up to 9 times production increase resulted based on a dimensionless productivity index.