In this paper we demonstrate the advantages of a new multicomponent induction wireline instrument to measure true horizontal and vertical resistivities utilizing a field data example. These data were incorporated in an enhanced shaly sand tensor resistivity petrophysical analysis and resulted in an approximate 20% increase in calculated gas-in-place reserves over the previously used methodologies. Petrophysical results agreed well with conventional routine core analysis and production well test data. 3DEXSM Rh and Rv and conventional wireline log data were acquired in a deep marine turbidite sequence. The example well contained significant volumes of thinly bedded, laminar silty shales and high porosity gas sands that were deposited over very high quality massive channel and turbidite fan complex sands. A high anisotropy ratio, Rv/Rh, indicated the presence of high quality laminar sand pay in a 37-meter interval above the more massive gas-bearing sands. This was qualitatively confirmed by resistivity and acoustic imaging logs. The initial results of effective porosity, and effective water saturation (Indonesian) petrophysical analysis utilizing Array Laterolog deep resistivity (SFR 50–inch depth) data resulted in anomalously high water saturations and poorer apparent reservoir quality in these thinly bedded shaly sand intervals. A second analysis was performed utilizing both horizontal and vertical resistivities in a tensor resistivity model. The laminar shale volume calculated from the 3DEX resistivity data agreed well with NMR-derived shale volume from clay bound water (CBW) data. These results were used in a Thomas-Stieber volumetric model to determine the final laminar-dispersed shale distribution and laminar sand total porosity. Laminar sand resistivity was also calculated from the 3DEX horizontal and vertical resistivity data and used in a Waxman-Smits water saturation model to determine the true laminar sand water saturation. This analysis indicated that the laminar sands were generally of similar quality as the more massive sands. The tensor resistivity analysis indicated a low water saturation in the laminar sand section and is consistent with a capillary water saturation model in a dry gas reservoir. The increase in hydrocarbon saturation resulted in a significant increase in the initial GIP (Gas-In-Place) estimates. Two subsequent production well tests, comparable on a roughly equal net sand basis, choke size, and flowing tubing pressure, confirmed that the laminar sand section was capable of flowing gas at rates similar to the more massive sands without significant pressure draw down. The addition of true vertical resistivity combined with horizontal resistivity in a tensor petrophysical model provides additional new information about laminar shale volume and laminar sand resistivity in thinly bedded, hydrocarbon-bearing reservoirs. Utilizing a true volumetric petrophysical model and determining the laminar-dispersed shale distribution results in a more accurate shaly sand reservoir characterization and, as demonstrated in this example, resulted in a significant increase in hydrocarbon volume evaluated.
Field and numerically simulated data show that coplanar induction measurements (σxx and σyy) are affected by both conductive and resistive muds. The effect is, for a resistivity contrast of 10 or less between the formation and mud, approximately proportional to the resistivity contrast. The borehole effect is generally stronger for a decentralized tool. In the perpendicular eccentricity mode, the eccentricity effect on σxx or σyy can be greater than 100% of the true formation responses. We demonstrate that dual‐frequency processing can reduce the eccentricity effect by an order of magnitude. We investigate the effect of invasion for both circular and elliptic invasions. For circular invasion, the effect on σxx, σyy, or the coaxial measurement (σzz) is characterized by a critical invasion thickness. For invasion thinner than the critical thickness, the effect is minimal. The effect increases rapidly as invasion thickness increases beyond the critical thickness. For elliptic invasion, both the σxx and σzz responses are similar to those of the corresponding inner circular invasion. Beyond a long‐to‐short‐axis ratio of three, an elliptic invasion behaves like a long, thin fracture.
Drilling technology for oil and gas exploration has evolved continuously based on feedback from operational experience. With the operators' focus on drilling more challenging unconventional wells, the biggest drivers are efficiency and operating cost. Operators want more real-time information during drilling to provide early warning of potential problems and take corrective actions. Service providers are meeting these challenges with technology improvements that are more robust and automated. The main focus for service providers is improving reliability throughout the service life of the tool while reducing maintenance cost. Consequently, in the past few years there is growing interest in the oil and gas industry towards developing technology and tools to gather more real-time downhole data and use analytical algorithms for fault diagnostics and health prognostics of components in drilling systems. This paper develops the framework and algorithms for constructing data-driven component life models and utilizing them to optimize operational efficiency and extend the life of the drilling system. The key driver behind this approach it to minimize the overall life cycle cost of tools which includes the cost of maintenance and cost of failure. The optimization variables are maintenance intervals and operational parameters (e.g. rpm, weight on bit, etc.) that should be tuned to achieve a desired level of drilling efficiency and reliability. Mathematical models for predicting the life of critical components in the drilling system is developed a-priori by using design qualification test data, operational data, drilling dynamics and historical FRACAS (Failure reporting analysis and corrective action system) information. The framework developed in this paper utilizes these predictive life models for making operations and maintenance decisions at various stages during the life cycle of the tools. The methodology developed in this paper is used to optimize the operational parameters and maintenance intervals for two designs of the bottomhole assembly namely (a) rotary steerable system without motor and (b) rotary steerable system with motor. Tradeoff of maintenance cost and operational performance is studied for different level of operational parameters. The results presented in this paper show that significant improvements in operational efficiency and maintenance intervals can be optimized by using downhole operations and predictive analytics.
B. Sh. Singer, O. Fanini, K.-M. Strack, L.A. Tabarovsky, Western Atlas Logging Services, 10201 Westheimer, Houston, TX 77042, USA, and X. Zhang, Electrical Engineering Dept., University of Houston, 4800 Calhoun Rd., Houston, TX 77024, USA Abstract Through casing resistivity measurements confirmed the original concept proposed by Alpin (Ref. 1) and recently revived and improved by Kaufman (Ref. 2) and Vail (Ref. 3). A commercial tool can be used for monitoring producing wells, waterflooding control, and searching for bypassed hydrocarbons in abandoned and active wells. The information on the resistivity of the formation is represented by the second spacial derivative of the casing voltage that is generally small. This makes the evaluation of possible distortions arising from different kinds of casing imperfections important. These imperfections include casing collars, corrosion, perforations, etc. The fact that only low frequencies can be used for the measurement allows us to propose fast and accurate modeling algorithms. Numerical evaluation shows that the distorting effect of casing imperfections is quite moderate. Typically, it does not exceed 10–20% of the measured apparent resistivity. The vertical resolution of the measurements is limited by the spacing between the voltage sensing electrodes. It can deteriorate due to the cement sheath that always exists around the casing. A significant distortion of the measurement occurs near the bottom of the casing. This distortion can reach 50% of the signal. To improve the readings, a simplified inversion algorithm has been developed. The most direct application of the algorithm is the monitoring of the pay zone resistivity. Introduction One of the major requests from the oil and gas industry to logging service companies is the measurement of the formation resistivity behind steel casing. Formation resistivity is the primary indicator of water, gas, and oil saturation. The through casing resistivity (TCR) tool would allow the industry to control pay zone depletion, waterflooding, etc. It would also make it possible to log producing and abandoned wells targeting the hydrocarbons bypassed in the open hole logging operations. Two factors are impeding application of the traditional logging approaches to measurement of formation resistivity behind a steel casing. The first and the major factor is the low resistivity of the casing steel that is typically about 0.2 m. A high magnetic permeability of the steel (40–110) is another obstacle for electrical logging of cased wells. At the frequency of 1 kHz, the skin depth in the steel is less than 0.1 cm; much smaller than the thickness of the casing wall. This means that an electromagnetic field created inside the casing will not penetrate into the formation. To energize the formation and to measure its inductive response. Ref. 4 proposed to saturate the casing with a strong magnetic DC-field. The relative magnetic permeability of a saturated casing equals one. This results in the increase of the frequency threshold. Ref. 5 proposed very low-frequency induction logging measurements so that magnetic saturation could be avoided. A number of authors concentrated their efforts on the development of a TCR tool based on low frequency galvanic energizing of the casing and the formation behind the casing. The concept of evaluating the current leaking from an energized casing into the formation was originated by Alpin (Ref. 1), who proposed a three-electrode apparatus measuring the second difference of the voltage inside the casing. As a practical solution, the concept was not implemented for almost 50 years, mainly due to two circumstances. P. 999
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.