Remote Real-Time Well Monitoring and Model Updating Help Optimize Drilling Performance and Reduce Casing Strings
- Roger Bisham Goobie (Schlumberger) | Edward Tollefsen (Schlumberger) | Sheila Noeth (Schlumberger) | Colin Michael Sayers (Schlumberger) | Lennert den Boer (Schlumberger) | Pat Hooyman (Schlumberger) | Goke Akinniranye (Schlumberger) | Jay Cooke (Helis Oil &Gas) | Ron Thomas (PPI Technology Services) | Edgar Carter (PPI Technology Services)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- September 2008
- Document Type
- Journal Paper
- 242 - 249
- 2008. Society of Petroleum Engineers
- 1.6.1 Drilling Operation Management, 1.11 Drilling Fluids and Materials, 1.6.3 Drilling Optimisation, 2 Well Completion, 3 Production and Well Operations, 5.3.4 Integration of geomechanics in models, 5.1.8 Seismic Modelling, 1.2.1 Wellbore integrity, 5.1.6 Near-Well and Vertical Seismic Profiles, 1.12.2 Logging While Drilling, 5.5.3 Scaling Methods, 1.1.2 Authority for expenditures (AFE), 1.7.5 Well Control, 1.2.2 Geomechanics, 1.6 Drilling Operations, 5.6.1 Open hole/cased hole log analysis, 5.1.5 Geologic Modeling, 1.2.3 Rock properties, 1.7 Pressure Management, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 4.3.1 Hydrates
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Remote real-time pore pressure monitoring using a combination of Logging-While-Drilling (LWD) services coupled with a predrill pore-pressure model reduces risk and cost by providing significant insight into wellbore stability and allowing for casing seat optimization. This paper presents the results of a shelf job in the Gulf of Mexico (GoM) that allowed an operator to drill successfully in a very tight hydraulic envelope and even eliminate a string of casing.
The uncertainty in the pore-pressure prediction ahead of the bit can be significantly reduced by model updating. The LWD measurements allow the predrill velocity-to-pore-pressure transforms to be updated while drilling using the velocities from the sonic tool and pressures from the LWD formation pressure tool. This calibrated transform is then applied to revise the predrill pore-pressure model while drilling, and thus provide an estimate ahead of the bit. In this case study, the predrill model used interval velocities extracted from a 3D mechanical earth model of the northern GoM based on velocities derived from checkshots and sonic logs. These velocity data were kriged to give a 3D velocity model over the entire northern GoM with uncertainty estimates.
Using state of the art LWD technologies, a new methodology was used to optimize drilling performance on a well in Vermillion Block 338. Continuously updated LWD annular pressure measurements effectively gauge wellbore pressures and help the driller rapidly intervene in pressure and/or geomechanical wellbore stability issues. A complete understanding of the hydraulic forces acting on a borehole can increase the rate of penetration, provide greater safety, minimize casing strings, reduce or eliminate kicks and formation fracturing, and allow faster and less expensive completions.
The techniques described in this paper using real-time measurements allowed the operator to extend both the 9 5/8-in. intermediate casing and 7 in. liner to TD. As a result, a critical casing string was pushed 1,287 ft deeper than planned and a pre-planned 5 in. liner eliminated. This saved casing expense, as well as slim-hole drilling and completion costs.
Introducing real-time LWD formation pressure measurements and pore-pressure prediction to the drilling workflow can reduce wellbore stability uncertainty during the well construction process. Failure to maintain annular pressures within the hydraulic operating range of the pore-pressure and the fracture gradient can compromise the ability to push casing seat points as deep as possible. If this limitation is not properly mitigated, it can and may significantly increase project cost.
The drilling performance on a well in Vermillion Block #338 was optimized by applying a method that sends real-time streaming data received from the downhole tools through mud-pulse telemetry via satellite to an Operation Support Center (OSC) for real-time drilling operations. OSC personnel monitored and updated the wellbore hydrodynamics and mechanical earth model, incorporating observations made during drilling. The results along with mud weight recommendation were then sent to the rig, and the appropriate action was taken to ensure that the surface mud weight, the equivalent circulating density (ECD), and the equivalent static density (ESD) were kept within the limits of the pore pressure and fracture gradient.
In general, most operators use wireline formation pressures and interval velocity data to update the compaction-driven pore pressure model at the end of the drilled section. This technique is often used in areas such as the GoM where compaction disequilibrium is the most important cause of overpressure (Bourgoyne et al. 1986). This methodology works well in young, fine-grained sediments, particularly where the lithology remains similar (in composition and grain size) throughout the section drilled.
The limitations of using this technique on wireline are:
1. The formation pressure data are not available in real-time while drilling.
2. An operator may not account for variations and/or divergence in the actual pore pressure from pre-drill pressure prediction models. When this happens, operations are often constrained by an approval for expenditure (AFE) that does not include an extra logging run to validate real-time pore pressures. Drilling without this information often results in well stability problems, kicks, increased stuck-pipe potential, and often, a substantial increase in well costs.
3. The computed pore pressure can be either under- or over-estimated by a significant amount, if the velocity-to-pore-pressure transform is not correctly established. The former can lead to avoidable well control incidents, while the latter can impede optimal casing point selection and reduce the chances of completing the well in the target reservoir.
The critical success factor for the Vermillion well was the combination of real-time LWD technology and continuous communication between the rig and the OSC. Rapid analysis of the LWD sonic and formation pressure data allowed for re-calibrating the velocity to pore-pressure transform, thus reducing the uncertainty of the look ahead geopressure model.
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