The Impact Of Completion Related Pressure Losses On Productivity In Shale Gas Wells

Abstract

Transient linear flow diagnostic plots in shale gas wells often exhibit a positive y-intercept and may mask the early transient linear flow regimes because of non-reservoir pressure drops. Increased completion resistance reduces the peak production rate early in the life of a well impacting NPV. The shale gas industry is very early in the research required to distinguish the individual contributions of completion resistance, e.g. poor fracture conductivity, near-perforation damage or choke skin, and fracture face damage skin. Many of these phenomena can be diagnosed in production wells using unique shape(s) from various diagnostic plots allowing for analysis of completion effectiveness.Mechanistic reservoir simulations were used to generate diagnostic plot signatures for low conductivity fractures, choke skin, and near fracture face damage. Subsequently, the corresponding signatures were compared with a large database of shale gas wells in numerous plays across North America to aid in the fingerprinting of these non-reservoir pressure losses. Only low fracture conductivity, not choke skin, can have a quarter slope. Near fracture face damage results in two distinguishable linear trends, one of the damaged region and the other for the matrix.Completion skin diagnosis is a way of evaluating fracture efficiency by identifying the root causes of the non-reservoir pressure losses so as to mitigate them in the future. The following presents a catalogue of signatures that enables greater diagnostic capabilities to classify non-reservoir pressure losses. The study is the first comprehensive cause-by-cause look at completion damages with an emphasis on identification and diagnosis in shale gas wells.

Analyses of Processes, Mechanisms, and Preventive Measures of Shale-Gas Reservoir Fluid, Completion, and Formation Damage

“…Jackson and Rai (2012) describe the sources of skin effects involved in hydraulically-fractured shale gas wells completion efficiency caused by various completion resistances. These issues are reviewed in this section.…”

“…Non-Newtonian apparent viscosity effects also may be important (Li et al, 2012). A fracturing-fluid clean-up inefficiency skin, water entrapment or blockage pseudo-skin, or multiphase pseudo-skin, s mp , results from the water-blockage due to hybrid relative permeability jail effects of the gas-water fluid system (Jackson and Rai, 2012).…”

“…Bennion (2002) and Reiniche et al (2013) explain that the stress-induced mechanical interactions between the proppant and reservoir formation fracture surface can cause proppant embedment into the near-fracture-face formation matrix, formation grains deformation, proppant and formation grains crushing, disintegration, and fine particles generation, and subsequent pore plugging in the compacted near-fracture face formation, the near-fracture face reduced permeability region can capture the fine particles internally during production. Near-fracture face pseudo-skin, s fs , resulting from proppant-embedment is given by (Jackson and Rai 2012):…”

“…Near-wellbore fracture choking effects cause choke or near-perforation pseudo-skin, s ch , resulting from poor connection between the fracture and the wellbore because of particle deposition expressed by (Jackson and Rai, 2012):…”

Do Perforated Completions Have Value for Engineered Geothermal Systems

“…Jackson and Rai, 2012, [41] have come closest to proposing methodologies for discriminating various types of apparent skin in shale gas plays -including low conductivity fractures (manifested by a ¼ slope), poor connection to the wellbore (choke skin and near fracture face damage), relative permeability effects, fracture skin and casing connections; using the apparent skin intercept concept. They reiterated concepts for poorly connected factors strictly using standard choking analogs [see for example Cinco-Ley and Samaniego, 1981 [29].…”