Shale Formation Re-Fracturing; Why do it, What is Needed and How?

Multi-fractured horizontal wells in Shale plays exhibit, sometimes dramatic, performance decline due to deterioration in completion efficiency. This decline is caused by one or more of the following physical processes:

Loss of effective fracture area due to crushing of the unpropped fracture length and near closure of that part of the fracture
Reduction in conductivity due to proppant embedment under increasing closure stresses on the fracture surfaces
Reservoir rock creep
Permeability reduction under decreasing reservoir pressure
These processes cause an adverse impact on the effective fracture dimensions and are controlled by pressure changes:

Bottomhole Flowing Pressure – a local parameter at the wellbore
Near wellbore pressure drop – an intermediate range parameter
Far field reservoir pressure drop – a global parameter
The decline in the well performance is controlled by the way we drawdown the wells especially in early times. Looking back at historical production practices suggests that the industry practices may have damaged the hydraulic fracture effectiveness. The damage starts at the wellbore and spreads deeper in the reservoir as production time increases. In some cases, wells are drawndown so severely that tensile formation failure and casing damage happen very early in the life of the well as outlined by Suarez-Rivera, et.al.6.

In order to overcome the reduced effective fracture dimensions, it is necessary to evaluate the performance of the multi-fractured horizontal wells and its remaining potential and the impact of re-fracturing. This can be achieved by RTA, PTA and developing an analog for the potential uplift with re-fracturing.

In this webinar we discuss an analog model, developed from a statistically significant dataset of over 80 wells in the Haynesville Shale, for estimating the economic value, the potential uplift and the minimum threshold volume required. We also discuss methods to achieve this potential including implementation. Some of these points were presented by Jacobs7 in a JPT article.

Further, for relatively mature shale plays, production optimization becomes critical to maintain volumes. Re-stimulation represents a significant production optimization opportunity to partially reverse completion effectiveness decline and enhance volumes. Re-stimulation could potentially lead to production acceleration; by re-opening the fractures, and enhanced reserves; by creating new stimulated volumes.

Technical Contributions:
The work is novel in the way it demonstrates:

Concept of an effective analog to quantify potential value and economic viability of active re-stimulations
Workflow for quantification of production uplift from passive re-stimulation
Procedure for optimizing the timing and benefit from future candidate re-stimulation
Fracture design to achieve effective re-stimulation of multi-fractured horizontal well