Cement Resistivity and Implications for Measurement of Formation Resistivity Through Casing

Klein, James D.; Martin, P.R.; Miller, A. E.

doi:10.2523/26453-ms

Cited by 3 publications

(1 citation statement)

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“…One initial concern was the potential for corrosion (rust) on the outer casing and cement surrounding the casing to electrically isolate the casing from the earth. However, oil‐field cement typically has resistivity in the range of 1 to 8 Ωm (Klein, Martin, and Miller ), which is more conductive than the background earth resistivity considered here. As to rust on the casings, measurements made by Marsala, Hibbs, and Morrison (), where one source electrode is on the surface and a second electrode is inside a well, would not be possible if casing corrosion were limiting current flow into the earth.…”

Section: The Modelmentioning

confidence: 99%

Hydro‐frac monitoring using ground time‐domain electromagnetics

Hoversten

Commer

Haber

et al. 2015

Geophysical Prospecting

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A B S T R A C TAs motivation for considering new electromagnetic techniques for hydraulic fracture monitoring, we develop a simple financial model for the net present value offered by geophysical characterization to reduce the error in stimulated reservoir volume calculations. This model shows that even a 5% improvement in stimulated reservoir volume for a 1 billion barrel (bbl.) field results in over 1 billion U.S. dollars (US$) in net present value over 24 years for US$100/bbl. oil and US$0.5 billion for US$50/bbl. oil. The application of conductivity upscaling, often used in electromagnetic modeling to reduce mesh size and thus simulation runtimes, is shown to be inaccurate for the high electrical contrasts needed to represent steel-cased wells in the earth. Finescale finite-difference modeling with 12.22-mm cells to capture the steel casing and fractures shows that the steel casing provides a direct current pathway to a created fracture that significantly enhances the response compared with neglecting the steel casing. We consider conductively enhanced proppant, such as coke-breeze-coated sand, and a highly saline brine solution to produce electrically conductive fractures. For a relatively small frac job at a depth of 3 km, involving 5,000 bbl. of slurry and a source midpoint to receiver separation of 50 m, the models show that the conductively enhanced proppant produces a 15% increase in the electric field strength (in-line with the transmitter) in a 10-m background. In a 100-m background, the response due to the proppant increases to 213%. Replacing the conductive proppant by brine with a concentration of 100,000-ppm NaCl, the field strength is increased by 23% in the 100-m background and by 2.3% in the 10-m background. All but the 100,000-ppm NaCl brine in a 10-m background produce calculated fracture-induced electric field increases that are significantly above 2%, a value that has been demonstrated to be observable in field measurements. I N T R O D U C T I O NHydraulic fracturing of reservoirs has been used in the hydrocarbon industry for over 50 years. With the recent onset of high production from unconventional reservoirs, its use has significantly increased. Efficient production of hydraulically fractured reservoirs requires accurate prediction of the extent and active surface area of fractures or fracture networks that are created and/or activated. Micro-earthquake *

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Section: The Modelmentioning

confidence: 99%

Hydro‐frac monitoring using ground time‐domain electromagnetics

Hoversten

Commer

Haber

et al. 2015

Geophysical Prospecting

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Measurement of Formation Resistivity Through Steel Casing

Singer¹,

Fanini²,

Strack³

et al. 1995

All Days

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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

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Looking Behind Casing: Evaluation and Application of Cased-Hole Resistivity in Saudi Arabia

Al-Ajmi

Al-Shahri

et al. 2004

SPE Asia Pacific Oil and Gas Conference and Exhibition

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Logging through casing is an important measurement for reservoir surveillance in mature fields. In the last 70 years, thousands of producers have been drilled in Y field, Saudi Arabia, and many are producing water.Successfully identifying by-passed oil and monitoring oil/water movements are critical for successful management of the Y field.In this study, cased-hole formation resistivity (CHFR * ) was field tested and evaluated in two wells in the Y field and in a third well in Z field. The three tests cover the following conditions; carbonate and shaly sand reservoirs, vertical and horizontal wells, and oil producing and water injection wells. In general, the CHFR measurements agree well with the openhole wireline and LWD logs. In low and high resistivity reservoir intervals, differences were observed. To address these differences, CHFR theory is reviewed and application conditions of CHFR logging are discussed. Guidelines for future CHFR jobs are presented. Run in small tubing Need slim tool Washed-out holes DOI Flowing wells Hold-up Fluid contacts in hole C/O analysis Near wellbore effects DOI Deviated wells Acid effect High Σ LithologyThe main applications of CHFR are: (1) to re-evaluate existing fields by locating by-passed hydrocarbon, (2) to monitor movement of gas/oil, gas/water, or oil/water contacts, (3) to monitor reservoir saturation changes with time, and (4) to provide resistivity log in difficult-to-drill wells where openhole log is not available.To introduce a new tool such as CHFR into Saudi Arabia, however, extensive field tests and evaluation are normally required. This report summarizes the CHFR test results in Y field and an application example in Z field, including: (1) test of CHFR in a carbonate oil reservoir in well Y-472, (2) test of CHFR in the carbonate oil reservoir swept by injected water in well Y-457, and (3) application of CHFR in well Z-321 where more than 1000' of LWD resistivity and gamma ray data in a shaly sandstone oil reservoir was lost due to LWD tool malfunction. # Color code in Table 1: Black -not recommended. Grey -use with caution.White -recommended. Csalt -concentration of salt (salinity). DOI -depth of investigation. In many situations, the tool measurements are complementary.

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Cement Resistivity and Implications for Measurement of Formation Resistivity Through Casing

Cited by 3 publications

References 0 publications

Hydro‐frac monitoring using ground time‐domain electromagnetics

Hydro‐frac monitoring using ground time‐domain electromagnetics

Measurement of Formation Resistivity Through Steel Casing

Looking Behind Casing: Evaluation and Application of Cased-Hole Resistivity in Saudi Arabia

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