Enhanced Geothermal Systems – Promises and Challenges

Geothermal energy plays a very important role in the energy basket of the world. However, understanding the geothermal hotspots and exploiting the same from deep reservoirs, by using advanced drilling technologies, is a key challenge. This study focuses on reservoirs at a depth greater than 3 km and temperatures more than 150°C. These resources are qualified as Enhanced Geothermal System (EGS). Artificially induced technologies are employed to enhance the reservoir permeability and fluid saturation. The present study concentrates on EGS resources, their types, technologies employed to extract energy and their applications in improving power generation. Studies on fracture stimulation using hydraulic fracturing and hydro shearing are also evaluated. The associated micro-seismic events and control measures for the same are discussed in this study. Various simulators for reservoir characterization and description are also analyzed and presented. Controlled fluid injection and super critical CO2 as heat transmission fluid are described for the benefit of the readers. The advantages of using CO2 over water and its role in reducing the carbon footprint are brought out in this paper for further studies.

Estimate Gas Initially in Place of Tight Gas Reservoirs Based on Developed Methodology of Dynamic Material Balance Technique

With growing global demand for hydrocarbons and decreasing conventional reserves, the gas industry is shifting its focus in the direction of unconventional reservoirs. Tight gas reservoirs have typically been deemed uneconomical due to their low permeability which is understood to be below 0.1mD, requiring advanced drilling techniques and stimulation to enhance hydrocarbons. However, the first step in determining the economic viability of the reservoir is to see how much gas is initially in place. Numerical simulation has been regarded across the industry as the most accurate form of gas estimation, however, is extremely costly and time consuming. The aim of this study is to provide a framework for a simple analytical method to estimate gas. Usually during production three variables are readily accessible: production rate, production time, and pressure-volume-temperature properties. This paper develops an analytical approach derived from the dynamic material balance proposing a new methodology to calculate pseudo time, with an interactive technique. This model encompasses pseudo functions accounting for pressure dependent fluid and rock variables. With the dynamic material balance yielding weak results in the linear flow regimes, an additional methodology derived from the volumetric tank model has been taken into consideration whereby equivalent drainage area is linked to total reservoir area. It has been shown even with short production data this volumetric approach yields accurate results. This proposed methodology has been validated against previous literature and additional cases considered to determine the sensitivity of each of it to reservoir parameters. Finally, it is shown that this method works for both fractured and unfractured wells in tight gas reservoirs, however, it is sensitive to the quantity of data based within the pseudo steady state flow period.

Continuous Improvement in Well Delivery

The Bulla gas-condensate reservoir is located in the north-west side of Baku Archipelago, is one of the most complex high-pressure fields in the world, with close PPFG margins and reactive clay in the overburden. The objective of this paper is to share the experience of how the challenges in the overburden section are managed to achieve improvement in the well delivery, through the application of continuous learning approach and the use of new technologies. The Bulla wells are highly complex wells in the region. The overburden shales are young sediments 250 to 1200 m to be drilled and cased off with 24" casing, this has significant challenges such as slow ROP, Bit Balling and tight hole due to the shale swelling. These challenges can lead to issues such as stuck pipe and lack of zonal isolation. To overcome the challenges and similar cases in well delivery, continuous improvement (CI) techniques and new technologies were evaluated and applied in the project. The CI approach helped identify the issues in the delivery of the overburden and actions taken resulted in significant improvement in well delivery and reduced the risks. The issues were worked on, and most feasible solution was chosen. The improvement plan has been risk assessed for the challenges of handling large volumes, possible losses, spillage etc. and risk control actions are implemented. The next well was drilled with higher operational efficiency, cost optimization and better hole quality to achieve zonal isolation by proper placement of cement. Further improvements were planned for the next wells in the field, by extending under reaming range through the application of new technologies. For 18 5/8" casing, a hole size of 24" required, this was drilled using multiple trips due to tool limitations. By using the advanced drilling dynamics software, BHA along with the required under reamer identified tools and design the section was delivered in one run. The application of this approach will not only reduce the time and cost but will also will help to deliver a quality well bore. The study provides an overview of how CI can be effectively implemented to achieve the overall improvement in the performance of the well delivery. Additionally, it gives insight on how new technologies in BHA design and reaming can improve the drilling performance.

Numerical Simulation of Natural Gas Hydrate Exploitation in Complex Structure Wells: Productivity Improvement Analysis

About 90% of the world’s natural gas hydrates (NGH) exist in deep-sea formations, a new energy source with great potential for exploitation. There is distance from the threshold of commercial exploitation based on the single well currently used. The complex structure well is an efficient and advanced drilling technology. The improvement of NGH productivity through various complex structure wells is unclear, and there is no more complete combing. Thus, in order to evaluate their gas production characteristics, we establish a mathematical model for exploitation of NGH, and then 13 sets of numerical models based on the geological parameters of the Nankai Trough in Japan are developed and designed, including a single vertical well, a single horizontal well, 1~4 branch vertical wells, 1~4 branch horizontal wells, and 2~4 branch cluster horizontal wells. The research results indicate that wells with complex structures represented by directional wells and multilateral wells can significantly increase the area of water and gas discharge, especially cluster wells, whose productivity can be increased by up to 2.2 times compared with single wells. Complex structural wells will play an irreplaceable role in the future industrialization of NGH.

Accuracy of Guided Surgery and Real-Time Navigation in Temporomandibular Joint Replacement Surgery

Background: Sophisticated guided surgery has not been implemented into total joint replacement-surgery (TJR) of the temporomandibular joint (TMJ) so far. Design and in-house manufacturing of a new advanced drilling guide with vector and length control for a typical TJR fossa component are described in this in vitro study, and its accuracy/utilization was evaluated and compared with those of intraoperative real-time navigation and already available standard drilling guides. Methods: Skull base segmentations of five CT-datasets from different patients were used to design drilling guides with vector and length control according to virtual surgical planning (VSP) for the TJR of the TMJ. Stereolithographic models of the skull bases were printed three times for each case. Three groups were formed to compare our newly designed advanced drilling guide with a standard drilling guide and drill-tracking by real-time navigation. The deviation of screw head position, screw length and vector in the lateral skull base have been evaluated (n = 72). Results: There was no difference in the screw head position between all three groups. The deviation of vector and length was significantly lower with the use of the advanced drilling guide compared with standard guide and navigation. However, no benefit in terms of accuracy on the lateral skull base by the use of real-time navigation could be observed. Conclusion: Since guided surgery is standard in implant dentistry and other CMF reconstructions, this new approach can be introduced into clinical practice soon, in order to increase accuracy and patient safety.

Robust Dynamic Toolface Calculation for Automatic Steering Control with Rotary Steerable Systems Under Extreme Conditions

Reliable toolface calculation is essential for achieving robust automatic steering control with rotary steerable systems (RSS). For RSS with fully rotating sensor packages, this task becomes particularly challenging under extreme conditions, where signal-to-noise ratio (SNR) of measurements from one or more sensors reduce significantly (e.g., while drilling near-vertical wells, along dip, towards magnetic north, in the vicinity of casing and/or under severe vibration and stick-slip). To ensure robust toolface control for fully rotating RSS under these conditions, this paper proposes a novel dynamic toolface calculation method. The proposed dynamic toolface calculation method of the new-generation fully rotating RSS overcomes the challenge of achieving robust toolface control despite extreme drilling conditions, by bringing together real-time health monitoring, online sensor calibration and novel sensor fusion techniques. Considering that robust toolface control is the heart of any drilling automation architecture with RSS, this technology is key to enable advanced drilling control strategies in the future.