Frac Hit Induced Production Losses: Evaluating Root Causes, Damage Location, Possible Prevention Methods and Success of Remedial Treatments

Abstract

Frac hits or "frac bashing" is a fracture-initiated well-to-well communication event that can create production losses (or gains), and on occasion, mechanical damage when frac energy from a stimulated well extends into the drainage area or directly contacts an adjacent or offset well. Pressure increases have been detected in wells at distances ranging from hundreds to thousands of feet from the stimulated well. While these in-zone frac hit events do not pose an environmental problem if there is no failure of containment, there can be some alteration of the production potential in one or both of the wells involved. Frac hits along the preferential fracture plane were an uncommon but known event when the completion method only involved vertical wells, but the rate of incidence has increased sharply as the preferred completion method has shifted to relatively closely-spaced, multiple fractured horizontal wells (MFHW) in low permeability formations such as the mudstone rocks commonly referred to as shales. Mechanical damage within the well and success of methods of prevention, damage control and remediation will be examined by case histories and published contexts of incidents in several basins, but will not be the main goal of the paper. The primary effort will focus on examining causes of production loss and duration of the loss, including looking at production declines pre-hit and post-hit. Known causes include in-situ stress alteration potential, timing of fracture closure, near-wellbore proppant loss, liquid loading, rock-fluid interactions, sludges and wetting factors. Also considered will be geological effects such as regional fractures and linked natural fracture clusters. A main objective will be to identify pressure transient, chemical analysis or other monitoring techniques to identify location and type of damage. Remedial operations are most effective when the potential cause of production losses can be ranked probabilistically and the depth of the production-reducing event can be estimated as near-field or far-field. Analyzing this data will also assist in defining whether chemical or mechanical treatments such as refracturing or a hybrid treatment system may be the best approach.

Nonlinear Autoregressive Neural Networks to Predict Hydraulic Fracturing Fluid Leakage into Shallow Groundwater

“…In order to realistically assess the upward migration of fluids over the lifetime of a typical horizontal well, each simulation consists of six stages, namely, fracturing fluid injection, well shut-in, first production, second production, and abandonment. Firstly, a total volume of 11,356 m 3 of fracturing fluid [14] is injected into the domain during 2.5 days. Then, a 5-day shut-in period takes place.…”

“…Then, a 5-day shut-in period takes place. Afterwards, the production periods are modeled with outflow rates of 16 and 3.2 m 3 /day for an interrupted period of 2 and 13 years, respectively [14]. In the abandonment stage, the production is stopped.…”

“…The fluid flow along the abandoned well and at the overburden aquifer interface is monitored. Note that we used data reported in Brownlow et al [14], which are based on available industry data for the Eagle Ford Shale play in south Texas.…”

“…Migration of formation fluid and brine from a shale gas reservoir to overlying strata could occur through natural or anthropogenic permeable pathways, such as faults, fractures, and bedding planes and leaky abandoned wells, in the vicinity of fracturing operations [7][8][9][10][11][12][13]. Abandoned wells could be affected by frac hits, i.e., the interaction between hydraulic fractures and wells, and the steep pressure gradient associated with the operation [14]. The frac hit to an abandoned well may facilitate upward fluid migration, depending on the cement/wellbore integrity [15].…”

Workflow Development and Sensitivity Investigation of Offset Well-to-Well Interference Through 3-D Fracture Modeling and Reservoir Simulation in the Denver-Julesburg Basin

“…In addition to tighter well spacing, longer lateral lengths are being drilled with more stages, closer stage spacing, and greater fluid and sand volumes to further maximize production potential. The resulting outcome of this practice is increased interaction of fracture networks between wellsalso known as well "bashing" or "well-to-well" interference (King et al 2017). It is imperative that an understanding of the interaction between parent wells and child wells is developed and modeled to gain an understanding of the possible effects well "bashing" has on short-term and long-term production.…”