Gas saturation measurement in low-porosity sands*
R. Marsh A , R. Ansari A , D. Chace A and K. Boyle BA Baker Hughes.
B Chevron Australia Pty Ltd.
The APPEA Journal 51(2) 744-744 https://doi.org/10.1071/AJ10124
Published: 2011
Abstract
Traditionally, pulsed neutron data has been used to calculate water saturation and/or monitor gas/water contacts in zones of high formation water salinity. In low or unknown salinities carbon/oxygen measurements have been used for oil saturation measurements in porosities greater than 15%. In tight gas sands, porosities are typically less than 10% and are too low for either method to work. In gas sands with low or unknown water salinities and porosities below 15%, neither Sigma or C/O measurements will work. New pulsed neutron instrumentation and methodology are available for through-casing gas saturation measurements.
The new technology is independent of water salinity and enables gas saturation calculations to be made in porosities as low as 5%. The technique includes modelling that enables the tool response to be determined in advance. Modelling takes into account several factors, including: lithology, completion geometry, reservoir pressure, gas density and gas composition (for example: methane or CO2).
The measurements are sensitive to gas pressure in the reservoir, and this paper will discuss ways that the data can be used to infer the relative and, in some cases, absolute pressures of different zones. The data set presented straddles the gas/water contact in the borehole. The effects of re-invasion by the borehole fluids will be discussed with respect to the corresponding openhole and cased hole water saturations, from both inelastic and capture measurements.
Roger Marsh is applications engineering and geoscience manager for Baker Atlas in Perth, WA. He has more than 15 years of field experience in open and cased-hole services. Since 1995, he has overseen field trials for open hole and cased hole services including the RPM prototype and held various international technical and management assignments, most recently as Asia Pacific technical manager. |
Rafay Ansari is a senior geoscientist at Baker Hughes where he has been working on cased-hole formation evaluation since 2006. He received a Master of Science (petroleum engineering) from the University of Texas, Austin, in 2006 and a Bachelor of Science (mechanical engineering) from National University of Sciences and Technology, Pakistan in 2000. His prior experience includes working as a production engineer for an operator and as a project engineer for a consulting company. |
David Chace is the product line manager for cased-hole formation and production evaluation at Baker Hughes. Previously, he was project manager for horizontal production logging system development. He has held international assignments in the Far East and Middle East and was responsible for pulsed neutron and production logging applications and interpretation. He joined the Dresser Atlas (now Baker Atlas) pulsed neutron research group in 1980 to develop pulsed neutron logging instruments, interpretation methods and software. He has a Bachelor of Science (physics) from the University of Rhode Island. |
Keith Boyle received a Bachelor of Electrical Engineering from Carleton University, Ottawa in 1981. Since then, he has worked for Schlumberger and various operators in numerous locations before taking his present position as petrophysicist for Chevron. |
References
Ansari, R., Mekic, N., Chace, D., Rust, M., and Starr, M., 2009—Field applications of a new cased hole gas saturation measurement in tight gas reservoirs. SPWLA 50th Annual Logging Symposium, The Woodlands, Texas, 21–24 June. Paper: R.Gilchrist, W.A., Prati, E., Pemper, R., Mickael, M.W., and Trcka, D., 1999—Introduction of a new through-tubing multifunction pulsed neutron instrument. SPE Annual Technical Conference and Exhibition, Houston, Texas, 3–6 October, SPE 56803.
Inanc, F., Gilchrist, W.A., Ansari, R., and Chace, D., 2009—Physical basis, modeling, and interpretation of a new gas saturation measurement for cased wells. SPWLA 50th Annual Logging Symposium, The Woodlands, Texas, 21–24 June. Paper: M.
Marsh, R.J., Boyle, K., Ansari, R., and Chace, D., 2010—Application of new pulsed neutron technology in the low porosity, low salinity Cooper Basin of South Australia. SPWLA 51st Annual Logging Symposium, Perth, WA, 19–23 June. Poster: OO.
Trcka, D.E., Gilchrist, W.A., Riley, S., Bruner, M., Esfandiari, T., Ly, T., Shearin, D., Patino, T., Murray, H., Potter, J., Rose, R., Chen, J., Olsen, S., Lovera, O., McCants, D., Berger, A., Ellsworth, K., Barolak, G., Martin, R., McFall, A., and Guo, P., 2006—Field trials of a new method for the measurement of formation gas using pulsed neutron instrumentation. SPE Annual Technical Conference and Exhibition, San Antonio, 24–27 September. SPE 102350.
