Moving From Wireline Logging to Logging-While-Drilling in an Aggressive North Sea Drilling and Formation Evaluation Program—A Case Study of the Brenda Accumulation

Moving From Wireline Logging to Logging-While-Drilling in an Aggressive North Sea Drilling and Formation Evaluation Program-A Case Study of the Brenda Field Michael Dawber; Michael Dawber PathFinder Energy Services, Inc. Search for other works by this author on: This Site Google Scholar Ewan Mitchell; Ewan Mitchell PathFinder Energy Services, Inc. Search for other works by this author on: This Site Google Scholar Dan Barson Dan Barson OILEXCO Incorporated Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, October 2005. Paper Number: SPE-96716-MS https://doi.org/10.2118/96716-MS Published: October 09 2005 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Dawber, Michael, Mitchell, Ewan, and Dan Barson. "Moving From Wireline Logging to Logging-While-Drilling in an Aggressive North Sea Drilling and Formation Evaluation Program-A Case Study of the Brenda Field." Paper presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, October 2005. doi: https://doi.org/10.2118/96716-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Annual Technical Conference and Exhibition Search Advanced Search AbstractLWD was integrated into an aggressive drilling program to assess the Brenda field from a previously un-appraised discovery in the Central North Sea. In a six well drilling program in 2004, shifting the logging program from wireline to LWD facilitated a rapid but detailed evaluation of the Brenda accumulation with considerable time and cost savings. Originally single, vertical wells with wireline were planned but practice evolved into drilling 3-legged directional wells using full LWD suites to maximize information garnered per well.Using LWD enabled logging suites to reach TD in directional wells on first attempt and meant logging in-gauge hole rather than the washed-out hole suffered by the wireline tools due to drilling reactive shales with water based mud.Sophisticated LWD toolstrings including a formation pressure tester and a slow shear sonic tool were used in addition to the standard triple-combo (resistivity/density/neutron). Applying advanced data processing methods including phase velocity processing and a physics-based dispersion correction of the sonic as well as thin-bed processing of the resistivity facilitated quality control and quantitative use of the LWD data.The LWD formation tester was used to estimate the oil gravity and to accurately identify the depths of the oil-water contacts. This was required to identify the main Brenda East and Brenda West stratigraphically-trapped accumulations and also for reserves estimates. Downhole fluid sampling was not necessary in these wells.The LWD sonic measurements were used to refine the seismic models with accurate measurement of compressional and slow shear velocities in the overburden. This improved the top reservoir pick which is very important in a stratigraphic trap such as Brenda. The compressional and shear velocities measured in the reservoir were used to refine the acoustic impedance models. This meant that a costly VSP/Check shot survey was not required. This was fortunate because the only check shot survey that was run became stuck in the reactive formations above the reservoir.Thin-bed modeling of the resistivity logs helped derive a more accurate reserves estimate by providing horizontal and vertical true resistivities in a series of thin-beds in the "abandonment facies" above the main reservoir. Thin-bed modeling effectively increased the resolution of the LWD resistivity tool.Introduction and Geological SettingSince acquiring Block 15/25b in the Outer Moray Firth, North Sea, Oilexco Incorporated of Calgary, Canada has undertaken a rapid appraisal of the Brenda accumulation. Six wells were drilled in 2004 alone, giving, with sidetracks, a total of 12 penetrations of the Upper Balmoral sandstone reservoir. Figure 1 shows the reservoir at Brenda and the penetrations drilled to date. The Upper Balmoral sands were deposited 56 million years ago during the late Paleocene. At this time, sand and mud eroded from the uplifted Orkney-Shetland platform drained east into the subsiding basins of the Moray Firth and the Central and Viking Grabens creating a large complex of Tertiary channels and fans, which includes Brenda as well as the Forties fan to the south. At Brenda, three phases of deposition are recognized in an overall fining upwards sequence:Initial substrate scour followed by aggradational sand infilling, which created channel bases often lined with hemipelagic clays, followed by subsequent aggradation and backfilling with sand.2) Subsequent confined debris flow and high-density turbidite deposition created massive sandstones with scattered planar and laminated bedding.As sand supply waned, the channel sands were capped by thinly laminated sand and claystone beds that represent an "abandonment facies". Finally deep water clay deposits were draped over the underlying sand. At Brenda the "abandonment facies" has a limited distribution but where present the thin sands constitute pay. Total reservoir sand thicknesses up to 150 ft occur comprised of numerous flow cycles - each representing an individual pulse of sediment influx. Figure 2 is a schematic diagram illustrating the environment of deposition at Brenda. Keywords: main reservoir sand, log analysis, well logging, accumulation, abandonment facies, overburden, brenda accumulation, reservoir, society of petroleum engineers, upstream oil & gas 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.

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