Geo-stopping with Resistivity Forward Modeling to Prevent Drilling into the Loss Circulation Zone of a Prolific Carbonate Reservoir
- Keng H. Kok (Halliburton Energy Services Sdn Bhd) | John Pruimboom (Halliburton) | Frank David (Sarawak Shell Bhd) | Jit-Chiun Then (Shell Malaysia)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 2005
- Document Type
- Journal Paper
- 276 - 280
- 2005. Society of Petroleum Engineers
- 1.12.2 Logging While Drilling, 1.6.1 Drilling Operation Management, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 5.1.7 Seismic Processing and Interpretation, 1.6.7 Geosteering / Reservoir Navigation, 5.1.5 Geologic Modeling, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6 Drilling Operations, 5.8.7 Carbonate Reservoir, 4.1.2 Separation and Treating, 1.14 Casing and Cementing, 1.11 Drilling Fluids and Materials, 1.7.5 Well Control, 4.1.5 Processing Equipment
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The field-development plan for a Sarawak Shell Bhd.-operated gas field,located in the South China Sea offshore Sarawak, Malaysia, specified drillingof horizontal wells into the Tertiary-Miocene carbonate reservoir. The wellswere planned as high-capacity producers with a big-bore, long-casing flowdesign.
The traditional well design dictated that before entering the reservoir acasing had to be installed to stabilize the hole in soft shale. The uncertaintyof detecting the formation top resulted in a premature casing commitment of atleast 30 ft true vertical depth (TVD) above the top of the reservoir and theneed to use an expandable liner to cover 300 ft of exposed shale above thereservoir.
To obviate this problem, the capability of one of the components in thelogging-while-drilling (LWD) tool array, specifically theelectromagnetic-wave-resistivity (EWR) forward-modeling technique, was used todetect the top of the carbonate formation (i.e., the top of reservoir),immediately before drilling into it. A standard LWD tool is configured toprioritize EWR forward-model response as the carbonate-formation top isapproached. This configuration, together with an appropriately designedbottomhole assembly (BHA) and well trajectory, enabled the successfulimplementation of the plan to stop drilling approximately 1 ft TVD above thecarbonate top.
At this point, a conventional 9?-in. casing string was set at an optimumdepth.This eliminated potential well-control problems, costly remedialactions associated with lost circulation, and inferior cementation of the9?-in. casing string.
Thereafter, the wells were drilled horizontally in a conventional mannerinto the carbonate-gas reservoir.
This paper compares predrilling EWR forward modeling of the proposed welltrajectory with the actual well data while drilling. The predrilling- andpost-drilling-modeled data are presented.
The cost savings from employing this technique are variable, ranging fromsubstantial—in the event of a well-control situation and attendant highlosses—to moderate if the need to set an expandable liner is eliminated.Aminimum of U.S. $1 million per well was saved with this technique.
Sarawak Shell Bhd. operates numerous gas fields in the central Luconia arealocated in the South China Sea, offshore Sarawak, Malaysia.Thefield-development plan for the M4 field specified drilling two horizontal wellsinto the Tertiary-Miocene carbonate reservoir.The wells were planned ashigh-capacity producers with a big-bore, long-casing flow design.
In the central Luconia area, the drilling of development wells ischallenging because frequent mud losses or total loss of circulation areencountered as a result of the karst phenomenon, which is the secondary erosionof limestone formation producing subterranean fissures, conduits, and cavernsas well as fractures in the carbonate reservoir.
The carbonate reservoir is overlaid with a thick layer of soft shale, whichneeds to be drilled with high mud-weight drilling fluids: 13.27 ppg. A 9?-in.casing string has to be set before drilling into the carbonate reservoir toavoid borehole collapse when drilling into the reservoir with lower mud weightto prevent severe mud losses.Because the shale section above thecarbonate reservoir lacks any geological character or marker beds to helpdelineate the top carbonate, it was common practice to set the casing point atleast 30 ft TVD above the top carbonate.Subsequent drilling leftapproximately 300 ft of exposed soft shale along the borehole before enteringthe carbonate reservoir, which necessitated the installation of an expandableliner to isolate the soft shale.
Therefore, a new methodology was sought to minimize the length of theopenhole shale section.
|File Size||1 MB||Number of Pages||5|
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