BHA and Drillstring Modeling Maximizes Drilling Performance In Lateral Wells of Barnett Shale Gas Field of N. Texas

Abstract

The Barnett Shale field of North Texas is one of the most prolific and fastest growing natural gas fields in North America with a multi-trillion cubic feet equivalent upside potential. However, the area presents numerous drilling challenges. In the vertical section, roller cone bits had unacceptable low penetration rates while PDC bits suffered premature damage. High torque and drag along with low penetration rates hampered drilling the curve and lateral sections. To address these challenges, a detailed engineering analysis was performed utilizing sophisticated BHA and drill string modeling software. Engineers studied offset wells and drillstring modeling including buckling load analysis, critical speed analysis, and torque and drag analysis. As a result of the study, engineers determined that bit whirl and stick-slip were resulting in premature bit damage and reduced ROP while drillstring buckling resulted in inefficient transfer of weight on bit. Modeling helped design a BHA that mitigated buckling while optimized drilling parameters avoided critical speeds. The improvements resulted in 42% to 121% higher penetration rates with minimal damage to the PDC bits. The 8¬3/4" vertical section was drilled in one PDC run in 60 out of 104 wells resulting in significant reduction in rotating hours and average cost per foot. The new BHA reduced drillstring buckling and significantly reduced torque and drag while drilling the curve and lateral sections. The authors will describe the significance of applying principles of buckling load and torque and drag analysis; to design technically sound BHA's. They will also discuss how to utilize drillstring dynamics to avoid critical speeds. Introduction Low porosity along with other geological/lithological challenges has hampered the efficient extraction of natural gas from the Barnett Shale for over 40 years. During the last several years, the operator has been utilizing fracturing technology which has significantly increased production in the field.[1] Drilling lateral sections further enhanced production/economics in the region (Figure 1). On an average, a horizontal well produces triple the cubic feet of gas compared to a vertical well at only twice the cost. Building on this success, the operator contacted a leading service provider to identify opportunities for improving drilling performance. To meet the operator's aggressive drilling schedule and achieve performance improvement, the team developed a strategy that included optimizing drilling methods to improve horizontal well delivery time. The goal was to achieve a significant increase in ROP drilling the vertical, curve, and lateral intervals. Geological Background The Fort Worth Basin (Figure 2), is a shallow, north-south elongated trough encompassing approximately 15,000 square miles in north-central Texas.[2] The basin is bounded on the north, northeast, and east by faulted basement uplifts of the Red River Arch, the Muenster Arch, and the Ouachita Structural Front. The southern limit is defined by the Llano Uplift.[2] To the west, the basin shallows onto the positive feature of the Bend Arch. The Fort Basin contains a maximum of 12,000 feet of sedimentary section in its deepest area adjacent to the Muenster Arch.[2] In this area, the Barnett section can reach a thickness greater than 1,000 feet.[2] In the core area (Figure 3) of the Newark East Barnett Shale Field, the Barnett shale is encased by tight carbonates which act as fracture barriers during the completion process.[2] A typical stratigraphic column of the Fort Worth basin is depicted in Figure 4. Drilling Optimization Process Structure Drilling optimization has resulted in significant improvements in drilling performance in the region.[3–5] The structure of the drilling optimization process followed by the service company is show in Figure 5. This process is comprised of four phases: pre-project, planning, drilling, and post-well. Each phase consists of clearly defined steps and peer review Figure 5.

Unlocking the Shale Mystery: How Lateral Measurements and Well Placement Impact Completions and Resultant Production

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