Optimum mud window prediction is very crucial for drilling any well. Accurate prediction of pore pressure, fracture pressure and other geomechanical parameters such as stresses, rock mechanical properties and finally the collapse pressure are key for designing the optimum mud window and effective well planning. Predrill predictions of pore pressure and wellbore stability become more and more challenging as the industry is moving to more and deeper and ultra-deep water wells. This is primarily becaue of lack of offset calibration together with inherent probrems and challenges associated with deep water environments. A substantial amount of nonproductive time (NPT) was associated during the initial phases of drilling campaigns in the Brunei deepwater. Accurate mud weight window prediction using regional scale pore pressure prediction and geomechanical modeling clearly demonstrated a significant reduction in nonproductive times over the different phases of drilling campaigns till date. This also includes a regular update or refinement of the model as soon as new data or information becomes available. This paper presents some of the methodologies employed during well planning and construction with refinement along the way, resulting in improvement on pore pressure and geomechanical model. Our intent is to document and share our experiences and lessons learnt in Brunei deepwater well so that design and execution workflow can be continuously improved thus the well can be delivered safely and costeffectively.
Mishra, Vinay K. (Schlumberger) | Barbosa, Beatriz E. (Schlumberger) | LeCompte, Brian (Murphy Oil) | Morikami, Yoko (Schlumberger) | Harrison, Christopher (Schlumberger) | Fujii, Kasumi (Schlumberger) | Ayan, Cosan (Schlumberger) | Chen, Li (Schlumberger) | Dumont, Hadrien (Schlumberger) | Diaz, David F. (Schlumberger) | Mullins, Oliver C. (Schlumberger)
Copyright 2014, held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors. This paper was prepared for presentation at the SPWLA 55th Annual Logging Symposium held in Abu Dhabi, United Arab Emirates, May 18-22, 2014. ABSTRACT Knowledge of formation fluid viscosity and its vertical and lateral variations are important for reservoir management and determining field commerciality. Productivity and fluid displacement efficiency are directly related to fluid mobility, which, in turn, is greatly influenced by fluid viscosity. Therefore, viscosity is a critical parameter for estimating the economic value of a hydrocarbon reservoir and also for analyzing compositional gradients and vertical and horizontal reservoir connectivity. The conventional methods for obtaining formation fluid viscosity are laboratory analysis at surface and pressure/volume/temperature (PVT) correlations. However, deducing viscosity from correlations introduces uncertainties owing to the inherent assumptions. Surface viscosity measurement may be affected by irreversible alteration of the sampled fluid through pressure and temperature changes, as well as related effects of long-term sample storage. A new downhole sensor for a wireline formation tester tool has been introduced to measure the viscosity of hydrocarbons.
Suppiah, Sitham (Murphy Oil) | Ahmad, Afidah (Murphy Oil) | Alderson, Christopher (Murphy Oil) | Akbarzadeh, Kamran (Schlumberger) | Gao, Jinglin (Schlumberger) | Shorthouse, James (Schlumberger) | Khan, Ifadat Ali (Schlumberger) | Forde, Chris (Schlumberger) | Jamaluddin, Abul (Schlumberger)
A technological breakthrough in the well construction process was recently accomplished in the deepwater Gulf of Mexico. An 11-3/4" O.D. liner was successfully installed through a whipstock window cut into a 13-5/8" casing. It was the first documented attempt worldwide to run casing larger than 10-3/4" O.D. through a 13-5/8" window.
The job's success can be attributed to thorough planning of well site operations and computer modeling of the proposed installation. The primary components of the planning activity included 1) analysis of available casing exit systems, 2) modeling of the bending and compressive loading on the 11-3/4" liner connections, and 3) detailed modeling of the drag expected during liner running operations both through the whipstock and into the deviated hole to total depth.
Murphy Exploration & Production Company was planning delineation drilling of their Medusa Prospect in Mississippi Canyon Blocks 538 and 582 (Figure 1). The operator had decided that the most economical option for delineation drilling was to sidetrack the existing wellbore to provide additional penetrations of the zone of interest. The casing program of the original well and the proposed bottomhole location of the delineation sidetrack dictated that the well be kicked off below the 16" casing shoe (Figure 2).
The operator decided that the evaluation program of the sidetrack hole include a conventional core. The core was necessary to fully assess the reservoir potential of the objective geologic horizon. Based on an analysis of the conventional coring systems available, it was determined that a minimum hole size of 8-1/2" was required to cut and recover a core large enough for adequate rock evaluation.
Initial sidetrack plans involved cutting and pulling the 13-5/8" casing just below the 16" shoe. This plan allowed running a casing program similar to the original well and drilling the required 8-1/2" hole at total depth even if a contingency drilling liner were required. The casing was mechanically cut at 5150' MD and attempts to pull it failed. A cement bond log had been run in the well prior to cutting and indicated that the pipe was relatively free.
The contingency plan for sidetrack operations was immediately put into place. Plans called for milling a 125' section in the 13-5/8" casing between the 16" shoe and the casing cut at 5150' MD. Section milling operations were successfully initiated and approximately 2' of casing removed when lost returns occurred. Since the mud weight utilized at the time could not be reduced due to well control considerations, section-milling operations were suspended and a balanced cement plug was placed inside the casing.
Given the constraints of sidetrack options now available and the required hole size at total depth, the operator was faced with two possible scenarios. The first involved cutting a whipstock window, setting the conventional 9-5/8" below and drilling a hole size less than 8-1/2" through the pay sand. This option would abandon conventional coring plans and compromise the formation evaluation objectives of the sidetrack. The second option involved cutting a whipstock window, setting an 11-3/4" liner below and allows drilling an 8-1/2" hole to total depth. This plan would achieve all the geologic and reservoir engineering objectives by allowing conventional coring operations.
The operator decided to pursue the second option if it were determined technically feasible. Equipment for both options was obtained to allow for a "fall back" position if it was determined that running 11-3/4" through and below the window was impossible or too risky.