May 5, 2017
The Right Approach to Proppant Flowback Control
Part 2 of a Series on Flowback Economics
In the preceding blog post, we took a look at the costs and causes of proppant flowback. Let’s continue the conversation around this expensive issue. Even after decades of research, operators often cannot predict when to expect flowback because there are numerous dynamics, including:
- Bottomhole formation closure stress and closure-stress rate
- Flowback rate and shut-in time after completion
- Fracture width, height, and tortuosity
- Proppant mesh size and angularity
- Proppant distribution inside the fracture
A quick re-visit to flowback costs
As we noted in the prior post, cleaning up and remediating proppant flowback cases during the first 2 years of a well operation can be expensive: $175,000 to $400,000 for a horizontal well; $50,000 to $150,000 for a vertical well. In addition to wellbore clean-up costs, the main cost is related mostly to replacing downhole equipment that’s irreparably damaged by proppant returning to the wellbore rather than remaining in place to prop open fractures in the reservoir.
A range of proppant flowback control measures, some more effective than others
We’ve talked to operators for decades about preventing proppant flowback. The range of measures they have employed across an enormous range of frac projects is extensive. Some have worked better than others. Here are the methods that have been most commonly applied and the typical outcome for each:
Choking—unreliable: Operators purposely flow the well back initially at reduced rate until the well produces hydrocarbons proppant-free. However, most of the time this is a short-term solution and as soon as the well is flowing back at regular rates proppants will start coming out, most of the time.
Forced Closure—unreliable: This procedure relies on fracture closure stress to “trap” proppant and hold it in place. The idea is by closing the fracture quickly, this process traps proppant in a uniform distribution. Unfortunately, the success rate is low and on certain occasions rapid fracture closure has led to additional proppant flowback problems.
Chopped fiber or thermoplastic strip—inconsistent. Based on enhanced friction between these materials and proppant grains, this approach is aimed at inhibiting proppant flowback. They haven’t proven consistently reliable. These techniques can also negatively affect fracture conductivity by restricting fluid flow.
Mechanical screens—inconsistent. These sand control screens prevent gravel-pack sandfrom flowing back up to the wellbore. Challenges include damage to the screen from fines or crushed proppant; scale build up and screen erosion caused by sand production.
Surface modification agent (SMA)—inconsistent. This liquid chemical is designed to link proppant grains together, but does not harden or set to build the required Unconfined Compressive Strength (UCS) to provide an effective crosslinked network under downhole conditions. With negligible UCS and a regular or high production rate, SMA cannot hold the proppant pack in place, which often leads to proppant flowback..
Liquid resin (LR)—inconsistent. LR can be coated on sand or other proppant at the wellsite. After it is pumped downhole, the UCS, is proportional to the liquid concentration added to the blend and the bottomhole temperature. Note that LR can negatively affect breaker and crosslinker performance.
Curable resin-coated proppant(RCP)—reliable. Operators have been preventing proppant flowback since 1976 by using curable resin-coated proppants manufactured under strict quality control conditions that ensure high UCS, increased conductivity and crush strength. At certain closure stress and bottomhole temperature and shut-in time, RCP grains chemically connect with each other and form a three-dimensional crosslinked network that prevents proppant flowback and all the associated expenses.
Curable resin-coated proppant is the proven method to control flowback costs
With the right completion design, operators can prevent proppant flowback. Curable resin-coated proppant, which sets downhole and stops proppant from coming back up to the wellbore, is the solution that has enabled operators to produce better wells for more than 40 years. A well completion with 100% curable resin-coated proppant (the most preferred) or a smaller resin tail-in percentage (usually between 25-50%) combined with high quality frac sand ensures operators can reduce their cost per BOE by reducing or eliminating costs related to proppant flowback remediation.View all posts