Donald L. Whitfill

Engineered LCM Design Yields Novel Activating Material for Potential Application in Severe Lost Circulation Scenarios

Particulate lost circulation materials (LCM) that work for severe-to-total losses are difficult, if not impossible, to find. Solutions that are effective for lower loss rates do not perform well at higher loss rates. Many LCM formulations have been used to treat severe losses, but their design and use has been more trial and error based mostly upon successful case histories. This paper describes the development of a combination of materials that is used in conjunction with other Engineered, Composite Solutions (ECS) to further enhance their performance. A novel combination of swelling materials, retarder, and fibers with a large aspect ratio is proposed as an activator that can be deployed with ECS typically available on the rig. The activator was designed and tested under conditions that qualitatively resemble severe lost circulation scenarios (large fractures). A shale swell meter was modified to qualitatively compare the swelling behaviour of different materials under different temperatures and retarder concentrations. A polyacrylamide-based swelling material was found to be sensitive to both temperature and retarder concentration. A newly sourced, potentially reservoir-friendly swelling material was found to be sensitive to temperature only. The activator-ECS combinations were tested for plugging capability with Permeability Plugging Apparatus (PPA) test equipment using different size tapered slots. Data from these modified PPA tests were used to determine the best combination of activator and ECS for plugging a particular-sized fracture simulated by the tapered slot. Field applications of systems that led to this proposed approach are discussed along with laboratory data comparing the swelling behaviour of different materials as related to mixing and pumping times. Introduction Lost circulation (Messenger 1981), the complete loss of drilling fluid in to the formation, is a perennial issue that translates to billions of dollars annually in NPT and cost of replacing the solutions. Solutions to arrest lost circulation, Lost Circulation Materials (LCM), are also well known and available. For many years, cost and local availability have been the primary driving forces behind the selection of LCMs. Solutions for drilling fluid losses sometimes also depend on formation type. In sandstone type formations, lost circulation through natural or artificial flow paths up to 2500 microns can be arrested with particulate LCMs. Numerous solution types and case histories can be easily found by a simple search on Onepetro. But dealing with lost circulation and providing solutions in formations with severe-total losses, requires planning, rigorous testing on existing solutions, and sometimes new solutions altogether. Due to various natural fractures or vugs, carbonate formations are another type which may require novel LCMs. Most of the time, particulate LCMs do not work in carbonate formations and some sort of chemical sealant solution is explored. On the other hand, increased demand for hydrocarbons has inspired the industry to explore hydrocarbon targets once considered unreachable. This has led to drilling deeper and in harsher environments. Lost circulation in such difficult environments just adds to the operator’s costs. In cases where both situations are present, like when drilling in highly fractured formations or in carbonate formations that are in deep, harsh environments, costs associated with lost circulation (NPT) increase dramatically. Hence it is prudent to invest time and resources in finding new LCMs, solutions, and LCM evaluation techniques that would help quantify LCM performance. Whitfill 2010, Kumar 2010, 2011, Savari 2011, 2012, and Kulkarni 2012, 2012 have demonstrated the advantages of looking into LCMs using new tools, new methods for testing, and new combinations of LCMs.

The Development of a Geopolymer-Based Pill as an Engineered Solution to Lost Circulation

Lost circulation is a common and highly varied drilling challenge. Whole fluid loss can be the result of entry into a highly permeable zone, vugular formation, or natural or induced fracture. Losses are further impacted by variables such as engineering practices, wellbore conditions, type of fluid (drilling, completion, cement, etc.) and formation properties. A variety of materials and techniques have been developed to stop lost circulation and stabilize the wellbore. One of the more common fluid solutions is the use of a dedicated pill formulation. These technologies may be comprised of particulate and/or fibrous material that is completely inert, or may be a chemically reactive solution that is triggered to form a sealant throughout the thief zone. Historically, these pills have proven highly effective, but most function under a narrow set of conditions. Another technical limitation for the materials used as a pill treatment is lack of structural integrity (strength) and a reduced tolerance to higher temperatures. This paper presents a comprehensive summary of the development of a new type of chemically reactive pill based on aqueous alkali alumino silicate as the key component. The aqueous alumino silicate is a low molecular weight, low viscosity solution that is sometimes referred to as a “geopolymer”. Set times can range from several minutes to several hours based on the type and concentration of setting agent. By controlling the type, size and quantity of particulate material in the chemically reactive pill formulation, properties such as density, temperature resistance, strength and flexibility can be regulated to suit a wide range of lost circulation challenges. Models were developed on factors affecting set times, as well as properties of the uncured and cured formulas. These results are utilized to design a lost circulation pill that could be easily pumped through a bottomhole assembly over a wide range of loss rates and downhole conditions. The alumino silicate pill can provide strength properties approaching those of cement with a corresponding tolerance of high downhole temperatures. The environmental characteristics of the system and the economics of its application are also presented.