Ultra-deep Resistivity Research Articles

Technology Focus: Offshore Drilling and Completion (October 2024)

The evolution of computational technology, coupled with the ability to digitize hardware and engage with end users, has enabled machine learning to enhance operational efficiency, safety, and cost-effectiveness in offshore oil and gas development. A key takeaway from recent literature is that, while automation tools have been present for years, their widespread adoption has been hindered by a lack of demonstrable financial benefits. To address this, the focus has shifted from mere deployment to achieving real value through significant cost savings, increased safety, and improved operational efficiencies (paper OTC 35137). Automation efforts in onshore operations prioritize efficiency, while offshore automation must focus on risk reduction and minimizing nonproductive time. For instance, a cutting-edge vessel-motion-prediction tool integrates advanced machine-learning techniques with metocean forecasts to enhance the reliability and safety of offshore drilling operations (paper OTC 35341). Paper OTC 35418 presents the importance of autonomous inflow-control devices in maximizing the production life of wells in deepwater West Africa, taking into account the various challenging reservoir conditions. Another critical insight from the research is the role of human intervention in the deployment of automation systems. Successful deployment requires iterative adjustments and feedback from operators to tailor systems to the specific needs of offshore environments. Collaboration among engineers, operators, and decision-makers is essential in refining these technologies to align them with operational goals and safety standards. Overall, these papers underscore the need for strategic adaptation of automation systems to the specific challenges of offshore environments. The success of predictive machine learning in this context depends on its ability to offer measurable financial benefits, improve safety, and drive operational efficiency. Recommended additional reading at OnePetro: www.onepetro.org. SPE 218473 Performance Optimization of Water-Injection Wells Using Autonomous Outflow Control Device Technology in Offshore Norway by G.F. Kvilaas, AkerBP, et al. SPE 218479 Use of Wired Drill Pipe, Along-String Measurements, and Advanced Logging-While-Drilling Imaging Enhances Wellbore-Condition Understanding and Improves Well Delivery Time, While Telemetry-Optimized Ultradeep Resistivity Measurements Enable Precise Geological Well Placement by Stephen Pink, NOV, et al. SPE 218360 Autonomous Restriction Navigation Through Wellbore in Wireline and Slickline Operations by S. DiPasquale, SLB, et al. OTC 35394 Intelligent Optimization of Ultradeepwater Oil-Transmission Risers Using an Enhanced Graph Neural Network by Hong Zhu, China University of Petroleum-Beijing, et al.

Holistic Approach Uses Electromagnetic Tools, LWD Data To Improve Reservoir Understanding

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 215519, “A Holistic Approach to Data Interpretation Combines the Strengths of Ultradeep Electromagnetic Tools With Shallow Logging-While-Drilling Data To Improve Reservoir Understanding,” by Karol Riofrio, SPE, and Nigel Clegg, Halliburton, and Luke Rawsthorne, Aker BP, et al. The paper has not been peer reviewed. _ During drilling operations, logging-while-drilling (LWD) tools, which have greater resolution than seismic, are deployed to aid in decision-making and optimize well placement. Focusing on the data sources in isolation can lead to successful wells, but placing this data in a geological context allows for more-sophisticated decision-making and leads to greater reservoir understanding. Key to linking the near-wellbore measurements with the geological models derived from seismic interpretation are ultradeep electromagnetic tools. The authors describe an approach in which all available technologies are combined to improve reservoir understanding of different depositional environments. Geological Background Deep marine turbidite deposits are recognized as an important hydrocarbon reservoir type; many recent major hydrocarbon discoveries and field developments worldwide occur in sediments deposited by turbidite currents. Turbidite deposits are characterized by a variety of elements such as large-scale erosive features, channels and channel deposits, overbank deposits, lobes, and channel/ lobe transition zones. Each of these elements contains distinctive characteristics. In this complex setting, better definition of the elements present in the reservoir significantly decreases uncertainty while drilling and can improve the completion design, lengthening well life. Applying different well-acquisition technologies such as ultradeep resistivity (UDAR) inversion and anisotropic inversion and interpretation methodologies such as petrophysical analysis, correlation with spectral decomposition volumes, and 4D seismic can help initially for well placement and subsequently for well-completion design and future development of analogous fields. Methodology The complete paper provides the background, characteristics, and advantages of the following methodologies that the authors used in the study: - 1D UDAR inversion - 3D electromagnetic UDAR inversion - 3D electromagnetic UDAR inversion for anisotropy - Spectral decomposition - 4D Seismic Case Study The strength of combining these tools can be demonstrated in the approach to understanding the results of a single well. In the target well, the main goal was to drain the remaining oil identified by 4D seismic in the target structure. Among the complexities acknowledged predrilling was an undulating oil/water contact (OWC) identified as a result of production from previously drilled wells in the area, the lithological complexity of the reservoir resulting from the turbiditic depositional environment, and the filling history of the field. Identification of these complexities highlighted that the chance of exiting the hydrocarbon-bearing zone was high because of the potential for structural uncertainty and a complex, undulating OWC.

3-D Adaptive Regularization Nonlinear Inversion of LWD Ultradeep Resistivity in Anisotropic Formation Based on Finite Volume Method of Secondary Field Coupled Potentials and Explicit Fréchet Derivative

3-D Adaptive Regularization Nonlinear Inversion of LWD Ultradeep Resistivity in Anisotropic Formation Based on Finite Volume Method of Secondary Field Coupled Potentials and Explicit Fréchet Derivative

Integration of Seismic Poisson Impedance Data with Real-Time Geomechanics and Real-Time 3D Ultradeep Resistivity Inversion Enabled New Opportunities in Developed Field: Case Study from Kuwait

Summary The Wara sandstone reservoir in the Minagish field of Kuwait Oil Company is a complex deposition of a typical pro-deltaic environment consisting of shaly-silty sandstone sequences, referenced as W7–W1. Three of these sequences (W6, W5, and W3) were expected in the case study well. The objective was to set a 9⅝-in. casing at the top of W6 and then drill through the Wara sequences to connect all of them and land and drill the lateral section within W3. The W6 sequence is typically the primary target in the Wara formation, being thick and consistent throughout the field. The next logical step in developing the Wara reservoir was to study and investigate the minor W5 and W3 members. Due to poor correlation of W5 and W3 channels in offset wells, the geological target was selected based on seismic Poisson impedance (PI). Historically, targeting the Wara formation occasionally resulted in multiple sidetracks due to drilling challenges. A real-time geomechanics service was used to overcome drilling challenges, and real-time 3D ultradeep resistivity inversion was implemented to optimize the well placement. An extensive predrilling study for geomechanical and ultradeep resistivity inversion modeling helped to develop a road map for an optimal and safe well-construction process. The study showed that use of real-time 3D ultradeep azimuthal resistivity (UDAR) inversion would help to optimize the well placement and maximize the sweet-zone exposure. The original well design, mud properties, and drilling parameters were modified based on the geomechanical study. Additionally, real-time geomechanics services were used to monitor and control the drilling process to follow the road map, which helped to avoid drilling issues, geostop at the W6 channel, and finally to run the casing smoothly. Real-time 3D ultradeep resistivity mapping in the lateral section helped the operator to drill through W6 and W5, land precisely, and drill the lateral in the W3 channel, which was well developed, as expected from seismic PI analysis. Formation evaluation of the lateral section showed an average porosity of 24 p.u., water saturation of 11%, and up to 3 darcies/cp mobility. The application of real-time 3D ultradeep resistivity inversion helped to triple the planned formation exposure and discover a geometric extension of the above deposited channels (W6 and W5), which will help for future field development. The flow test showed the highest production rates from W3 in the field. The integrated approach described above was recommended to be utilized for all future Wara wells.

UDAR: Past, Present, and Future: An Operator’s Experience and Perspective on the Challenges and Opportunities in Applications With Ultradeep Resistivity Tools

Proactive geosteering, landing, geostopping, geomapping, and look-ahead (LAH) applications of ultradeep azimuthal resistivity (UDAR) tools are becoming more common in operator new well delivery practices. In very specific and niche wells, almost exclusively high angle and horizontal (HAHZ), the value of information provided by these tools can significantly exceed the high cost of the service. In the past, UDAR technology was primarily used only for geosteering high-value, generally offshore horizontal wells, where the objective is typically to increase net pay. As time progresses, the application of UDAR has grown past HAHZ-limited applications to now include look around for geomapping and look ahead for geostopping. From an operator’s perspective, the justification for the high cost of UDAR is always challenged by not only the uncertainty of what the tool will deliver but what will be the reasonable actions based on the provided deliverables at the time of drilling. UDAR service companies seem to be in a depth of detection (DOD) “arms race,” but what operators really want is a greater understanding of uncertainty with the goal of better well delivery through confident decision making. One way to hedge this risk is to have a clear key performance indicator (KPI)-based pricing strategy, where vendor predrill study claims are tested during and after drilling, and compensation is based on their validation. Another limitation contributing to the underutilization of the UDAR service, and associated operator increased risk exposure, is the present-day inability for operators to verify predrill studies, real-time inversions, and post-drill interpretations via in-house modeling. Modeling is particularly important for the UDAR service, where the scientific and mathematical complexity of inversion extends far beyond human intuition. We believe that with the right application and pricing strategies, UDAR could grow past the high-value/high-cost portfolio of the past and be used on a more typical borehole assembly (BHA) in the future. In this paper, we will discuss our UDAR journey thus far, including reflections on past applications and present challenges, and we will propose some improvements, including standardization, that we hope the industry accepts to grow the quality and the number of future applications.

Mapping Complex Injectite Bodies With Multiwell Electromagnetic 3D Inversion Data

Electromagnetic (EM) inversion processing of ultradeep resistivity data has advanced from one dimensional (1D) to three dimensional (3D). These advances have helped improve the geological complexity that can be imaged and provide additional reservoir information. The large depth of investigation (DOI) of ultradeep LWD EM tools means that distant boundaries might not be detected by any other sensor in the tool string, making it difficult to verify the results. As inversion results represent a model of the subsurface resistivity distribution and not a direct measurement, it is important to have high confidence in the results. Directly comparing the component data measured by the tool to the modeled component data from the inversion across multiple frequencies provides confidence in the resultant model where the data have a close fit. However, as measurement sensitivities decrease with distance, there is potential for non-uniqueness, generating a model that is geologically unrealistic. Increased confidence can be achieved with independent verification of the model. This paper details results from a trilateral well in an injectite reservoir wherein the sand distribution was expected to be complex. The 1D inversions showed the vertical distribution of the sand, but the results were sometimes distorted by lateral resistivity variations. The 3D inversion of the data allowed the lateral resistivity variations to be resolved. These results can be corroborated by direct comparison with azimuthal resistivity images. Additionally, the laterals all diverged from the same main bore and remained close together initially in an area containing major sand injectites. The 3D inversions from two of the wells overlap and define similarly shaped structures, providing confidence in the 3D inversion model. In complex geobodies, such as the injectites described, significant lateral variation in the reservoir distribution is expected, which is not captured by 1D inversion. Understanding the shape of these structures and their potential connectivity using 3D inversion provides a major increase in reservoir understanding that is critical to completion design.

LWD for Imaging, Wellbore Placement, and Formation Evaluation

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 17646, "LWD for Imaging, Wellbore Placement, and Formation Evaluation," by J.C. Rasmus, SPE, C. Esmersoy, SPE, J. Seydoux, and A. Hawthorn, Schlumberger, prepared for the 2005 Offshore Technology Conference, Houston, 2-5 May. Logging-while-drilling (LWD) measurements are widely available for a variety of applications. Many of the first generation LWD measurements are similar to those obtained traditionally with wireline methods. However, there are measurements available now that are either complementary or are entirely unique compared with traditional wireline measurements. Introduction LWD borehole-seismic measurements can enable placing the bit on the seismic map or producing a seismic-impedance map ahead of the bit while drilling the well. These measurements provide accurate depth determination of drilling targets and identification of pore-pressure transgressions. LWD ultradeep-resistivity (UDR) measurement technology meets the requirements for geosteering at the reservoir level by use of subseismic resolution. Its major applications include delineation of the oil/water contact (OWC) and distance to reservoir caprock and bottom shale. Well Placement Since the emergence of LWD in the 1980s, the industry wanted a reliable while-drilling borehole-seismic measurement. However, several technical roadblocks prohibited its realization until recently. These difficulties included the nature of and required accuracy of the measurement, timing issues, sensors, automation, and the lack of an electrical connection between the downhole tools and the surface in a while-drilling configuration. Technological solutions to these road-blocks have since been found. Seismic-while-drilling data are delivered in real time to make critical decisions while a well is being drilled. They also replace intermediate wireline check-shot surveys, eliminating the need to stop the drilling process and pull drilling equipment out of the hole for the duration of a survey. Real-time accurate positioning of a horizontal borehole within a reservoir can be performed with standard LWD tools. However, a limitation of these measurements is the relatively small volume of investigation with traditional LWD sensors, which typically probe no deeper than 1 m into the formation. Therefore, unpredictable geological events are, in many cases, detected too late to allow proactive geosteering decisions. A prototype LWD resistivity tool was developed with a much larger radial response that allows detection of lithology features and fluid contacts that are tens of meters away from the borehole. The tool has a modular design with separate transmitter and receiver subassemblies that can be placed a large distance away, anywhere in the bottomhole assembly (BHA). The main output is estimated distance to boundaries indicated by resistivity contrasts. These distances are computed through inversion of a formation model in real time. On the basis of tool measurements, determining the optimum formation model and its related parameters allows proactive geosteering decisions and pro-vides significant geological insight into the reservoir structure.