Downscaling Geomechanics Data for Thin-Beds Using Petrophysical Techniques (2005)

Downscaling Geomechanics Data for Thin-Beds Using Petrophysical Techniques Kaibin Qiu; Kaibin Qiu Schlumberger Search for other works by this author on: This Site Google Scholar Robert Marsden; Robert Marsden Schlumberger Search for other works by this author on: This Site Google Scholar Yuri Solovyov; Yuri Solovyov Schlumberger Search for other works by this author on: This Site Google Scholar Muhammad Safdar; Muhammad Safdar Schlumberger Search for other works by this author on: This Site Google Scholar Olivier Chardac; Olivier Chardac Search for other works by this author on: This Site Google Scholar Mohammed Shatwan Mohammed Shatwan Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Middle East Oil and Gas Show and Conference, Kingdom of Bahrain, March 2005. Paper Number: SPE-93605-MS https://doi.org/10.2118/93605-MS Published: March 12 2005 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Qiu, Kaibin, Marsden, Robert, Solovyov, Yuri, Safdar, Muhammad, Chardac, Olivier, and Mohammed Shatwan. "Downscaling Geomechanics Data for Thin-Beds Using Petrophysical Techniques." Paper presented at the SPE Middle East Oil and Gas Show and Conference, Kingdom of Bahrain, March 2005. doi: https://doi.org/10.2118/93605-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Middle East Oil and Gas Show and Conference Search Advanced Search AbstractThin-bed sequences, especially those made up of alternating weak and strong sand layers with thickness of less than 1-ft, present a particular challenge in the generation of mechanical earth models (MEMs) for geomechanics design and analyses. Because these beds are thinner than the tool resolution, their heterogeneity and the variations between adjacent layers are often undetected by logging tools normally used to acquire geomechanics data. In other words, these tools cannot resolve the existence of alternating strong and weak sequences; they provide only averaged mechanical properties across these sequences.In one such case, an MEM and sanding study based on wireline sonic data indicated no tendency for sanding across a thick reservoir interval at the drawdowns required for economic oil production. The somewhat flat, log-derived curve of unconfined compressive strength (UCS) indicated that the entire reservoir was above the critical sand-free UCS state; however, laboratory data had revealed a large spread in UCS values, including rock strength values that are indicative of a significant sanding risk. In fact, the field had a history of solids production with depletion.Using the high-resolution images (with vertical resolution of 0.2 in.) provided by a microresistivity imaging tool across the same thin-bed intervals, and using alpha processing and other petrophysical log enhancement to further improve data interpretation, it was possible to generate a high-resolution (around 0.2 in.) porosity log. These downscaling techniques were combined with an empirical UCS-porosity relationship obtained from the available laboratory data. The resulting downscaled UCS log exhibited the wide range of strength values that were known to exist across the thin-bed sequence and were consistent with the history of sand production in the field.The remaining sanding evaluation for the well was completed using this integrated petrophysics and geomechanics approach. When the MEM and sanding analyses were extended to other wells in this field, the results matched well with the actual depletion curves and sanding history data.IntroductionThe Sarir field in Libya, operated by the Arabian Gulf Oil Company (AGOCO), has been experiencing progressively worse sand production problems in an increasing number of wells since 1984.[1,2]A geomechanics and sanding study initiated in 2004 investigated the probable cause of this problem and provided the information and interpretations needed to select an appropriate sand management solution, assist in future development decisions, allow appropriate completions planning, and optimize future reservoir management.To this end, the results of a data audit identified what geomechanics-related information existed that might be used to characterize previous sanding problems and diagnose their root causes. A laboratory testing programme using cores from the Sarir field obtained measurements of rock mechanics parameters relevant to stress modelling and sanding prediction. [3]Integrating laboratory results with other geomechanics information available from log, field, and drilling measurements provided an initial MEM. This MEM contained most of the information necessary for subsequent geomechanics analyses and sanding evaluations.[4,5]However, one significant finding was that routine UCS determinations from sonic logs in the Sarir field were unable to detect thin weak zones having thicknesses below the tool vertical resolution (i.e., 42 in.) of the sonic wireline tool. Therefore, petrophysical log-enhancement processing6,7 was conducted to obtain high-resolution, downscaled porosity logs using microresistivity image data. These data were then used to derive high-resolution (i.e., downscaled) UCS logs through UCS-porosity correlations. The UCS data from this process, which exhibited the same strength heterogeneities observed in the core data, provided the improved description of rock strength in the MEM that was needed in the subsequent sanding analyses of the thin-bed sequences. Keywords: reservoir, geomechanics data, correlation, upstream oil & gas, sarir field, depletion, spor, well logging, vertical resolution, resistivity Subjects: Formation Evaluation & Management, Open hole/cased hole log analysis This content is only available via PDF. 2005. Society of Petroleum Engineers You can access this article if you purchase or spend a download.