Refracturing on Horizontal Wells in the Eagle Ford Shale in South Texas - One Operator’s Perspective

Abstract

This paper outlines a refrac pilot testing program conducted in the Eagle Ford Shale.As wells in the Eagle Ford accumulate production over time and the pressure around the horizontal wellbore declines, it is important to also consider communication due to offset fracture stimulation. Refracturing trials in older fields, such as the Barnett Shale have yielded a positive enhancement of well performance (Siebrits et al., 2000). This paper evaluates the concept of diverting fluid and proppant along horizontal wells in the Eagle Ford, while considering any communication with older producing wells during refracturing operations.Pumping data acquired during the refracturing is used to explain some of these concepts. Modeling of induced fracture geometry, considering the effect of current pore pressures, is conducted with a fully three-dimensional hydraulic fracture numerical simulator. The pressure of the subject zone may affect the containment and rate of growth of the new fractures, as well as the re-orientation of the existing fractures.Refracturing an old horizontal well with 5,000 ft lateral length and more than 800 existing perforation holes in the casing is very challenging and requires a careful integration of reservoir knowledge, completions skills and experience. The technical team at Pioneer Natural Resources has developed an integrated workflow to design and execute a refracturing job for an Eagle Ford well. The work flow includes: 1) identification of the lower pressure areas along the lateral using surveillance data from the well, such as microseismic, tracer logs, and production data. 2) identifying which wells within the drilling schedule are offsetting older wells that have high cumulative production, and 3) designing a single fracturing job with several sub-stages separated by diverting agents. Each sub-stage is intended to target specific areas along the lateral, which were previously identified as low pressure zones. Volumes and pump schedules will be specific for each candidate and are based on but not limited to proximity to an offset well, lateral length, and existence of geological structures such as faults and fractures in the area. The results from this pilot testing program such as the radioactive tracers and the fracture gradient changes before and after refrac will be evaluated upon completion of the field execution.

Estimation of Optimal Frac Design Parameters for Asymmetric Hydraulic Fractures as a Result of Interacting Hydraulic and Natural Fractures - Application to the Eagle Ford

“…In this study we consider a specific well in the Eagle Ford shale described comprehensively in multiple Pioneer Natural Resources publications (Suliman et al 2013, Diakhate et al 2015. Figure 1C shows strong asymmetricity detected in the microseismic events where better stimulation is observed towards the heel (stages 5-9), less effective stimulation in the middle (stages 3-4) and moderate stimulation towards the toe (stages 1-2).…”

“…Figure 1C shows strong asymmetricity detected in the microseismic events where better stimulation is observed towards the heel (stages 5-9), less effective stimulation in the middle (stages 3-4) and moderate stimulation towards the toe (stages 1-2). The workflow introduced by Ouenes et al (2015) started by initially reproducing the bi-wing frac design used by Diakhate et al (2015) and then generated asymmetric half lengths constrained by geomechanics using a commercial frac design simulator. They built the bi-wing fracture model using the gamma ray, resistivity, effective porosity and the total organic content (TOC) logs (Diakhate et al 2015).…”

“…The workflow introduced by Ouenes et al (2015) started by initially reproducing the bi-wing frac design used by Diakhate et al (2015) and then generated asymmetric half lengths constrained by geomechanics using a commercial frac design simulator. They built the bi-wing fracture model using the gamma ray, resistivity, effective porosity and the total organic content (TOC) logs (Diakhate et al 2015). The rock mechanical properties were computed using the above input and surrogate logs.…”

Well Performance Simulation and Parametric Study for Different Refracturing Scenarios in Shale Reservoir

“…For refracturing through the existing clusters, a higher portion of microproppant is helpful to keep the narrow fractures created by refracturing open for improving gas production. It is the most common method to promote pumping rate, fluid volume, and proppant concentration in the previous successful refracturing jobs [29][30][31][32]. On the one hand, a higher pumping rate helps to reduce proppant collection at the bottom of the wellbore [6].…”

Response to Comment on “Comparison of Water Use for Hydraulic Fracturing for Unconventional Oil and Gas versus Conventional Oil”

“…Examples include studies of ∼20 wells each in the Eagle Ford and Bakken plays, 7 five wells in the Woodford play, 8 13 wells in the Barnett, 9 and one well in the Eagle Ford. 10 Two studies evaluated different screening tools to assess the potential for refracturing, suggesting that ∼15−20% of wells in the Barnett would be suitable for more in-depth analysis, 11 and another study suggesting that 6% of wells in the Barnett (11 out of 188 wells) would benefit from refracturing. 12 In summary, evaluation of refracturing is in the early phase of analysis with most studies converging to the conclusion that only a subset of wells will ever undergo the operation.…”