Well X is a deep-water exploration well whose main target is carbonate rock. Traditionally, drill bit records from adjacent wells or oil fields are the only major data source for drill bit selection. Usually, due to limited data availability, bit selection has been trial and error. However, now, Rock Strength Analysis (RSA) software is a requirement for pre-operation planning selection. Using logging data from adjacent wells, bit selection software based on unconfined compressive strength (UCMPS) calculations has been used to optimize the bit selection for Well X.
RSA software generates a comprehensive formation evaluation and bit selection analysis for drilling applications. Mud logs from adjacent wells are used to explain rock types. Some electronic logging with lithofacies analysis capabilities, such as gamma ray, compressed acoustic wave, density, neutron, and resistivity analysis, quantify the appearance of the rock and the percentage of depth. RSA software provides 18 rock types for analysis, from sedimentary rocks such as sandstone, claystone and limestone to hard igneous and volcanic rocks.
The choice of drill bits is based on their ability to drill into a certain degree of hardness. On the basis of this research, the compressed sonic logging is converted to shear sonic, and combined with the formation type, it can be used to calculate the UCMPS of the formation. In addition to drilling parameters, UCMPS is the main factor affecting the rate of penetration (ROP). UCMPS is also used to calculate the wear and impact index of the formation. The RSA application uses offset well data from more than 12,500 wells to select fixed or roller cone bits with appropriate cutting structure combinations, instrument protection, hydraulic configuration, and others based on the lithology to be drilled, rock UCMPS, formation wear and impact index. Key features.
Using RSA software, the formation characteristics of adjacent wells can be analyzed. In order to expand the scope of stratigraphic analysis, a comparative analysis of multiple wells in the surrounding oil fields in the same area was also carried out.
The polycrystalline diamond compact (PDC) bit selector in the RSA software considers the number of blades, tool size and blade profile of the bit on the basis of compressive strength, formation wear and formation impact. The harder the formation, the software will suggest using fewer blades and smaller tool sizes to improve the durability of the drill. If the formation is mainly composed of shale and clay rock, it will produce drill bit pilling signs, and the drill bit should have better hydraulic optimization to improve drill bit cleanliness. In order to reduce the risk of the drill bit being too thin due to wear, proper specification protection should be added to the drill bit.
After obtaining a general bit selection guide from RSA software, FEA-based modeling and simulation were performed to check the dynamic characteristics of drilling systems with certain bits. This kind of simulation is much more accurate than static BHA modeling because all components are individually modeled in detail. The simulation simulates the interaction between the cutting structure and the formation being drilled, using rock mechanics derived from the laboratory. The simulation result is the drilling behavior of all drill string components, including vibration, stress, torque, and even ROP prediction. The order of analysis of each part is
In this article, bit optimization is performed for 8.5 inches. And 6 inches. Partly included. For 8.5 inches. In part, two different bit designs were simulated using the basic BHA to determine the most stable bit. The first drill is a PDC with six blades and a double row of 16 mm cutters. The second drill has a single row of tools. The cutting structure model is shown in Figure 1.
The simulation was carried out with the WOB and speed parameters set at two different depths. On the basis of RSA analysis, limestone with UCMPS of 15-20 kpsi and shale with UCMPS of 2-5 kpsi are set as the drilling lithology in the simulation. Lateral, axial and torsional vibration; ROP comparison; then plot the build/down trend generated by the PDC bit and measurement while drilling (MWD) tool to find the most stable bit option.
The simulation shows that the single-row tool bit design (drill 2) is more stable than other bit designs (drill 1); the lateral vibration is much lower. These bits produce a similar stick/slip trend, but the value of bit 2 is slightly lower. In terms of ROP, bit 2 generally penetrates faster in carbonate formations and shale formations compared with bit 1. The up/down trend chart shows that both simulated drill bits can maintain the verticality of the well.
In order to obtain a road map of safe drilling parameters, a vibration threshold is set. Although the vibration generated by the drill bit 2 is small, the value is still considered high, especially the amount of lateral vibration of the drill bit. In order to minimize vibration, BHA optimization is necessary.
Previous simulations using basic BHA produced moderate to high lateral vibrations at the drill bit. If it lasts for a long time, this lateral vibration value will cause tool damage and low drilling efficiency. The threshold of vibration is set at a medium to high level. Multiple BHA options were simulated using the same parameters and drilling environment previously considered. The final optimization included changing the size of the stabilizer of the motor from 8⅜ to 8¼ inches, and reducing the motor bending shell from 1.15° to 0.78°.
The simulation using bit 2 and the optimized BHA produced a roadmap of safe drilling parameters that took into account the bit and all BHA components such as motors, stabilizers, and MWD tools.
This article was written by Special Publications Editor Adam Wilson and contains the highlights of the paper SPE 186264 "Rock Strength Analysis and Integrated FEA Modeling to Optimize Drill Bit Selection for Deepwater Exploration Drilling" by Yoan Mardiana and Bonar Noviasta, SPE, Schlumberger, 2017 SPE/IATMI Asia Pacific Oil and Gas Conference and Exhibition, Bali, Indonesia, October 17-19. The paper has not been peer reviewed.
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Journal of Petroleum Technology is the flagship magazine of the Society of Petroleum Engineers, providing authoritative briefings and topics about the advancement of exploration and production technology, oil and gas industry issues, and news about SPE and its members.
ISSN: 1944-978X (online) ISSN: 0149-2136 (print)