Early kick detection has been identified as being of primary importance in slimhole 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 slimholes to detect and confirm the presence of an influx rapidly. This system has been run successfully on a number of slimhole 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 values from the rig. The predicted values are derived from a model driven in real time by rig data such as pump rate and pipe rotation rate. Kick detection is based on deviations between measured data and idealized 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 for the 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 slimhole rig site.

High-fidelity trajectory estimation combined with dual-probe Measurement-While-Drilling (MWD) directional instrumentation provides a solution to minimum curvature’s known inefficiencies in modeling the true wellbore position and definition (Stockhausen & Lesso, 2003). While it may not be cost efficient to increase survey frequency from the industry standard of 30ft-200ft, it is possible using the techniques defined in this research to maintain current survey intervals and increase wellbore placement accuracy while reducing positional uncertainty by up to 45% over the most advanced commercially available magnetic survey correction algorithms. Taking advantage of modern MWD tool platforms enables the installation of an additional (30-inch) survey measurement probe in the existing tool string with a fixed and known offset to the primary survey probe. Directional surveys from both survey probes are telemetered to surface at traditional course length survey intervals in real-time. The two surveys along with the known steering and non-steering intervals are processed through a high-fidelity trajectory estimation algorithm to quantify the wellbore behavior between survey stations. The result is a highly accurate and dense survey listing with modeled trajectory waypoints between traditional surveys to reduce the course length between directional measurement datapoints and better capture the true well path. Through extensive lab modeling, it was determined that the use of the dual-probe MWD package in combination with the high-fidelity trajectory estimation algorithm could result in a reduction in the Ellipse of Uncertainty (EOU) by 20% in the horizontal (semi-major) plane and 45% in the vertical (semi-minor) plane when compared to Multi-Station Analysis (MSA) and BHA Sag survey correction techniques. In addition to proof-of-concept modeling, the system has been deployed and used in real-time application on three separate pads, totaling nine wells. The results were able to validate and exceed baseline goals by exhibiting, on average, a reduction of the EOU by 21% in the horizontal plane and 58% in the vertical plane. Further, True Vertical Depth (TVD) error at well Total Depth (TD) in excess of 10ft was observed on three out of nine wells (33%) in this limited real-time application study. This difference was relative to separate, concurrent processing of the surveys via Multi-Station Analysis (MSA) and BHA sag corrections. This level of increased TVD accuracy is significant in many applications, depending on zone thickness and difficulty of geological interpretation. Increased accuracy and reduced uncertainty result from a better understanding of the true well path between traditional course length surveys. The trajectory estimation algorithm quantifies the rotational build/drop and walk rates in real-time and is reinforced by the dual-probe directional survey measurements. These tendencies can be used to better project forward to the bit as the well is drilled. Improved projection to the bit allows for enhanced recognition of deviation from the well plan and better-informed steering decisions.