A significant percentage of all oil and gas wells drilled worldwide undergo a hydraulic fracturing program to stimulate production. In North America, a majority of new wells are fractured, particularly in the shale gas plays.

A variety of frac additive chemical service solutions are available to improve the performance of frac operations. Additives can deliver benefit during the frac job and during flowback and production operations, but not all frac additives are fully compatible with all formation chemistries, and incompatibilities between frac additive chemicals themselves have been known to cause significant problems. Any adverse reaction of fracturing fluid additives in-process or in the formation can negatively affect the economics of the frac job and post-frac production operations. A well-chosen frac additive program avoids such risks by considering the system as a whole as each challenge is addressed.

AddFRAC Friction Reducer provides a 17% reduction in pumping pressures.

Frac jobs today frequently require the use of millions of gallons of water for each fracturing stage. The water used is often obtained from multiple sources of varying composition and quality and is almost always heavily contaminated with bacteria and algae. Mixed sources of water can cause problems with scale precipitation, especially as the frac fluids commingle with formation fluids.

Varying source water composition also can affect the performance of friction reducers used to improve the efficiency of frac pumping operations.

Programs such as Baker Hughes’ AddFRAC Measurement and Control Services that offer complete frac additive options help take the guesswork and risk out of frac additive treatments. Complete solutions include provision of comprehensive application and monitoring programs to reduce formation damage caused by bacterial contamination, scale formation, and clay swelling. In addition, these services help use hydraulic horsepower more efficiently. They enhance water flowback, reduce costs, and improve production, allowing operators to better maximize their overall return on fracturing investment.

A particular challenge in frac jobs is the cost-effective control of bacteria and associated problems. Failure to control bacteria can result in contamination of the formation, production wells, and downstream portions of the system. These costly issues carry with them the risk of negative environmental impact and the potential for personal injury.

Effective bacteria management programs stop bacteria before they get established. The cost and health, safety, and environmental (HSE) benefits of this include prevention of reservoir souring, reduced biofilm fouling, lower corrosion failure rates, and reduced H2S scavenging requirements. Additionally, the health and safety challenges associated with handling produced H2S can be dramatically reduced if bacteria are well managed during frac operations.

Bacteria control begins with a complete understanding of the problem, across the entire system, including its source. A detailed microbiological survey allows for directed and cost-effective treatments. This helps maintain favorable economics both during the frac job and during the life of the producing assets.

A cleanup process is often an important starting point in bacteria management. Contaminated frac equipment should be cleaned between jobs to remove deposits that can harbor problem-causing bacteria. Cleaning makes it far easier to get consistent bacteria control at lower biocide loading rates.

Bacteria and algae are rampant in frac water sources. (Images courtesy of Baker Hughes)

The effectiveness of the biocide application should be monitored throughout the system. Testing involves an assessment of surviving acid-producing and sulfate-reducing bacteria populations, biocide residual concentration, H2S levels, and dissolved iron concentration. It confirms the efficacy of the program, and the data can be applied to future frac applications.

Bacteria control in the Fayetteville ensures fluid quality

In the Fayetteville Shale, an operator was experiencing bacteria and H2S problems that caused odor and black water issues in produced fluids. A comprehensive biocide program was prescribed that included a complete evaluation of system and treatment program performance.

Several frac water samples were collected to determine the sources of the bacteria problems. The bacteria in the field waters were exposed to various biocides. The optimal biocide was then subjected to additional testing to verify that it was compatible with other additives. Dedicated frac chemical injection trucks were deployed to ensure that all of the frac fluids were treated at the appropriate biocide concentration.

Adjustments in biocide program loading rates were made based on pre- and post-frac monitoring results.

Suitable fracturing fluid quality was maintained to prevent downhole biogenic sulfide production and its associated problems. By maintaining H2S levels below pipeline requirements, the customer gained a direct savings of approximately US $735,000 per year in H2S scavenging applications alone. Additional savings continue to be realized from reduced corrosion failure rates and lower HSE risk.

Scale control in the Bakken improves productivity

Mineral scale inhibition in post-fracturing operations of Bakken Shale wells is of great concern to several North Dakota oil and gas operators. In particular, subsurface production equipment needs to be protected against the choking effects of calcium carbonate, iron sulfide, and iron carbonate scales. As a key line of defense against scale, chemical inhibitors are often injected with frac fluids to afford protection during flowback. The key issue for operators is maximizing how long the flowback fluids remain treated.

To address the issue, a program was developed to mitigate the effect of difficult scales on post-frac production. With consideration for inhibitor efficacy in the presence of other additives and a thorough understanding of fluid chemistry and production parameters, a combination product was applied that could handle this challenging scale situation.

Post-frac monitoring revealed that the scale inhibitor level in the produced water flowback remained well above target for 327 days after the frac procedure. Scale deposition was well controlled over this extended treatment life, resulting in improved production, lower maintenance requirements, and reduced total cost of operating.

Sulfide abatement can impact lifting costs. Timely treatment can eliminate these expenses.

Treatment power is reduced in the Barnett

An operator producing in the Barnett Shale had been experiencing pressure problems during frac jobs, leading to higher horsepower requirements, longer pumping times, and added expense. The cause was frac additive incompatibility between the friction reducer and other crucial additives. Because the operator was sourcing additives from the frac pumping company and a chemical service provider, there was no effective way to predict or address chemical incompatibilities. The operator sought a single supplier to provide onsite support and a complete range of compatible additives to reduce costs and bring wells online sooner.

The operator’s primary goal was to maintain stable frac pressures within a suitable range to minimize pumping time and horsepower requirements. Product and service recommendations were provided based on water chemistry, measured bacteria populations, and reservoir pressures. Full laboratory support was deployed to ensure product compatibility before any chemical was applied.

Careful product selection and real-time application optimization delivered a 5 to 10% reduction in friction reducer injection rates. Biocide injection and scale inhibitor rates also were optimized, resulting in significant cost savings. Compatibility testing ensured that neither the biocide nor the scale inhibitor retarded the performance of the friction reducer. The operator was able to stabilize reservoir pressure spikes and maintain high injection rates.

A goal of every fracturing operation is to maximize and sustain reservoir production. Frac additive chemicals are vital to achieving this goal, and the ability of the service provider to manage the full life-cycle impact of frac additives is invaluable. A single point of contact in the provision of complete chemical programs can eliminate chemical incompatibility problems. And a comprehensive program that integrates monitoring and application services lowers risks, increases safety, and saves time and money.