Slimhole Early Kick Detection by Real-Time Drilling Analysis
- B.W. Swanson (BP Exploration) | A.G. Gardner (BP Exploration) | N.P. Brown (BP Research) | P.J. Murray (BP Exploration Operating Co. Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 1997
- Document Type
- Journal Paper
- 27 - 32
- 1997. Society of Petroleum Engineers
- 4.1.9 Tanks and storage systems, 1.12.6 Drilling Data Management and Standards, 1.6.3 Drilling Optimisation, 1.7.5 Well Control, 5.4.2 Gas Injection Methods, 1.11.5 Drilling Hydraulics, 5.3.2 Multiphase Flow, 1.11 Drilling Fluids and Materials, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6 Drilling Operations, 4.2 Pipelines, Flowlines and Risers, 5.6.4 Drillstem/Well Testing, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.12.3 Mud logging / Surface Measurements, 1.10 Drilling Equipment, 3 Production and Well Operations
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Early kick detection has been identified as being of primary importance in slim hole wellbores. Small annular volumes mean that to maintain the integrity of the well, allowable kick volumes must be small. Gas influxes must therefore be detected and shut in rapidly. This paper describes an early kick detection system developed for slim holes to detect and confirm the presence of an influx rapidly. This system has been run successfully on a number of slim hole operations.
The Early Kick Detection (EKD) System is based on real time analysis of drilling data obtained directly from a comprehensive mud logging system on the rig. The analysis technique compares predictions of mud flow out and standpipe pressure from a dynamic wellbore model with corresponding measured values from the rig. The predicted values are derived from a model driven in real time by fig data such as pump rate and pipe rotation rate. Kick detection is based on deviations between measured data and the idealised model predictions.
The EKD System has been incorporated into an operational engineer oriented graphical interface which has provided easy access to the model for both input and output of data and interpretation of results. This paper describes the design considerations and technology behind the EKD system and the engineering interface. The paper also presents examples of the system running in real time at a slim hole fig site.
Kick Detection in Slim Holes
There are a number of features unique to slim hole drilling that will determine requirements for any slim hole kick detection technology. The sensitivity of any kick detection system will be defined by the requirement to detect and shut in very small volumes of gas. The accuracy of the system will be defined by the degree of data scatter or noise introduced while drilling.
Bode et al  amongst others [2,3], have highlighted the importance of detecting a kick while it is sufficiently small that casing shoe pressures are not compromised during shut in and the subsequent well kill. The reduced annular volume of slim hole geometries severely limits the maximum allowable kick in a slim hole compared with a conventional wellbore. Indeed, the entry of what would be considered a small kick in a conventional hole can substantially reduce the mud hydrostatic in a slim hole. In a conventional 8 1/2"[0.216 m] hole 5"[0.127 m]] pipe annulus a one barrel influx will occupy a length of 22 ft [6.68 m] while the same volume in a 4 5/8" [0.121 m] hole with 3.65" [0.092 m] pipe will occupy 360 ft.[109.4m]. For a 10.8 ppg [1200 kg/m3] mud in this hole geometry this increase represents an additional 190 psi [1310 kPa] at surface on shut in.
To ensure shut in gas volumes in slim holes do not exceed the maximum allowable kick volume requires the use of a kick detection system with sufficient sensitivity to detect kicks considerably smaller than those identified by conventional technology. In conventional wells it is common to base kick detection on a pit volume increase of between 10 and 25 barrels [1.58 and 3.95 m ]. A similar detection limit for slim holes would have potentially hazardous consequences. At the start of this study it was recognised that an alternative kick detection system was required, one that would allow detection of a 1 barrel [0.158 m ] influx.
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