Environmental regulation has made drilling fluid selection increasingly difficult. Dr. James Gaertner describes a new water-based mud that balances performance and compliance.
There are two things the oil and gas industry can be certain of moving forward, they are that the demand for petroleum is going to continue to increase into the foreseeable future and, with that, the demand for environmental compliance. Recent events such as the Deepwater Horizon oil spill and the public debate on hydraulic fracturing, or “fracking”, have led to increasing environmental awareness. Pressure on regulatory agencies from concerned stakeholders has led to recent local restrictions in exploration and production activities in New York, Pennsylvania and Colorado and to support of more widespread and longer lasting measures from the EPA.
Despite these restrictions, the demand for oil and gas continues to increase at unprecedented rates and has largely been met by new technologies allowing the economic development of petroleum resources previously thought unattainable. Specifically, the use of hydraulic fracturing in conjunction with high-angle and extended-reach horizontal drilling has been used to allow development of unconventional shale resources. Today, more than 75% of formations being developed worldwide are considered to be in this group despite the technically demanding well designs required to reach the drilling objectives.
The combination of ever-increasing environmental regulation and sophistication of well design has made the selection of drilling fluids increasingly difficult. Operators face the complicated task of balancing environmental concerns and regulation compliance with the over-reaching goal to maximize well production, protect pay zones, and minimize potential damage to today’s sophisticated and costly rigs. Although conventional water-based muds (WBMs) are inherently environmentally friendly and have been used to drill thousands of wells, they many times fail to meet the high demands required to drill extended horizontal wells in reactive shale formations. On the other hand, oil-based muds (OBMs) are generally considered the benchmark for performance but are plagued by serious health, safety and environmental drawbacks that have led to restrictions of their use both on and offshore.
In order to address the need for a drilling fluid with high performance and environmental compliance several advancements have been made in formulations. Drilling fluids composed of low-toxicity, synthetic base oils (SBMs), such as esters, linear paraffins, linear alpha olefins and internal olefins, have been developed to help to address the environmental concerns of diesel-based OBMs while maintaining performance. These SBMs however, still fail to meet the restrictions of whole mud land farming, or discharge into the sea, and therefore require costly disposal. There are also still concerns about the toxicity of cuttings created while using SBMs, which have limited economical options for disposal in some cases. The development of high performance water-based muds (HPWBMs) has gained recent widespread use as another strategy to balance performance and compliance. HPWBMs differ from conventional WBMs in their use of polymers rather than bentonite clay to provide viscosity and API filtrate control. The use of polymers in lieu of clay increases the fluid’s resistance to contamination and allows for the use of a higher concentration, and wider range, of lubricants and shale inhibitors. Although HPWBMs adequately address the issue of environmental compliance, there is no clear consensus on whether or not they match the performance standards of OBMs.
The use of a Multi-Hydroxyl Alcohol (MHA) drilling fluid system was developed by ViChem Specialty Products specifically to bridge the gap between HPWBMs and SBMs. The MHA system is a hybrid between water-based and petroleum-based systems utilizing a novel approach to formulation. The MHA system utilizes the unique properties of the Multi-Hydroxyl Alcohol base fluid which acts as an environmentally friendly alternative to the diesel or synthetic base fluids used in emulsion based muds. Similar to synthetic or diesel based fluids, the MHA Base is composed of organic molecules that provide stability and performance characteristics comparable to petroleum base fluids. However, unlike petroleum products, the MHA molecules contain multiple hydroxyl groups allowing them to be dispersible in water without emulsification and completely nontoxic to the environment. The system is designed for horizontal drilling in reactive shales and has been successful in both the Marcellus and Eagleford formations. This combination of performance and compliance would be especially valuable offshore where regulations on the handling and disposal of drilling fluid are more stringent. The use of the MHA system is currently being evaluated for offshore drilling and it has been extensively tested in onshore brine based systems. (see table)
The use of saltwater in the formulation of drilling fluid creates several obstacles to use, which can include flocculation of clays and potential compatibility issues with viscosifiers, fluid loss additives and lubricants. The MHA system is formulated without bentonite and great care is taken to keep native clays to a minimum and inhibited from hydration through the use of solids control and shale inhibitors. All of this can help prevent the problems associated with unstable rheologies. The system is formulated to create stable properties and utilizes salt-tolerant polymers to provide viscosity and API filtrate control.
The use of lubricants in drilling fluids with high salinities can also create some unique issues in a drilling system. Incompatibilities of lubricants with divalent ions commonly associated with brines, such as calcium or magnesium, can cause formation of a grease-like precipitate. “Greasing out” of lubricant can reduce performance and potentially damage the formation. Some lubricants act like an emulsifier when coming into contact with even small amounts of oil in the system. This can cause inefficient operation of solids control equipment and feasibly damage the formation.
ViChem’s L-20 Lubricant has been extensively tested in high chloride drilling fluids and exhibits none of the problems associated with salt water systems. ViChem also has a popular coiled tubing lubricant for use with brine completion fluids that has been commercially available for several years without any known incident of greasing out or incompatibilities. Laboratory tests have confirmed field observations of its lubricity (see figure 1). Another potential use of compatible lubricants is in underbalanced brine drilling operations that are oftentimes performed in dolomite or limestone formations such as those found in the Bakken Shale or Austin Chalk. Both the MHA base fluid and the L-20 Lubricant have proven their ability to maintain their lubricating properties and compatibility with high chloride systems.
The complete MHA system includes formulations suitable for drilling salt strata that are prone to dissolution as well as formulations for use as sized-salt drill-in fluids that offer the highest possible protection for the payzone. Drilling with saltwater muds can be useful when the economics involved in using seawater or completion brines can offer a significant advantage over freshwater systems such as in offshore operations. Saltwater muds are also useful in preventing problems associated with drilling salt formations including wellbore erosion by dissolution and salt creep, which can cause excessive torque and packoffs.
Although it is oftentimes not seriously considered during the selection of drilling fluids, laboratory studies and field observations have shown the potential for drilling fluids to cause damage to the payzone in the form of reduced permeability. This can essentially reduce the overall lifetime production potential of a well. Although many wells drilled today are fracked after drilling is complete, it is good practice to use every possible precaution to maintain an unobstructed flow from the reservoir to the wellbore. Sized-salt systems can provide superior filtration and loss control as well as provide a high quality filter cake that is readily removed with fresh water or unsaturated brine washes.
By combining the performance characteristics of the MHA system with the capability to further protect the pay zone utilizing sized-salts, we can offer operators a sophisticated, alternative to WBM or OBM, system that has the highest possible return on their investment while exceeding the environmental compliance restrictions of today, and tomorrow.
Dr. James “Buddy” Gaertner is Director of Research and Development for ViChem Specialty Products in Conroe, TX. He has authored several technical papers and presentations on topics from drilling fluid performance to microbial contamination of drilling fluids. Gaertner worked as an environmental consultant on industrial air quality before joining ViChem and earned a PhD. in Aquatic Resources from Texas State University.