Kick Detection and Control in Oil-Based Mud: Real Well-Test Results Using Microflux Control Equipment

Abstract

Kick detection in oil and synthetic-based fluids has been a major concern for the industry for decades. Due to solubility issues, kick detection may be delayed and resulting well control operations may be problematic. Use of the Micro-Flux Control (MFC) method potentially offers a better way to address this problem in the same way it has been successfully demonstrated to work using water-based fluids (WBM). To check the performance of the MFC method while using oil-based mud (OBM), a series of full-scale tests were conducted at Louisiana State University PERTT Laboratory using natural gas injected into test wells containing an 11-ppg 70/30 diesel/water OBM. Performance results were compared with results previously obtained with WBM gathered at the same facility. The excellent and consistent character of the test results obtained encouraged the use of the MFC on a well to be drilled in Texas for Chevron. The well plan called for using OBM with mud density up to 17.4 ppg, at an anticipated depth of 13,000-ft. This would be the second well drilled with the MFC method, following one drilled in Brazil for Petrobras using WBM. The paper presents the results obtained during the one -week long live well testing at LSU as well as details of the first field test of the MFC system on the actual well drilled with OBM in Texas. The results confirmed the ability of the MFC system to detect very small influxes of natural gas into OBM with subsequent control of the influx accomplished in a way very similar to that used with WBM. Several other tests were also performed in both wells to explore possible additional uses of the MFC system. These included dynamic leak-off and formation integrity tests, behavior with multiple kicks inside the wellbore simultaneously, identification of ballooning or "breathing" during connections, and early detection of loss of circulation. All of the results obtained in both test scenarios confirmed the potential value of the MFC system for identifying and dealing with the above listed issues when conducting drilling operations utilizing OBM. Introduction Despite several challenges the industry faces when employing OBM, its use is still common. Environmental considerations are probably the biggest issue, but the technical advantanges offered by OBM in difficult drilling conditions often compensate for its choice. Today, OBM is the preferred choice for many wells located in deepwater, for HPHT applications, and for wells with chemical related wellbore instability. These challenging drilling scenarios have previously raised significant concerns related to detection of kicks and subsequent well control operations because of the solubility of natural gases in the hydrocarbon fraction of the fluid. Pit gain and increase in return flow rates are widely used as primary kick indicators. However, the roll and heave movements on floater drilling vessels and the relative inaccuracy of today's measurement methods may often result in high kick volumes in the wellbore. Gas solubility has been blamed for causing problems in early detection of the kick when using OBM. Previous studies done by O'Brien1, Thomas et al2, O'Bryan3 and O'Bryan and Bourgoyne4 have shown that there will be very little or no increase in pit level as the gas dissolves in the OBM over time and the detection of kicks is indeed more of a problem than in WBM. Cockburn5 added that "oil based muds with gas in solution, reduce the time the driller has to react to this potentially dangerous situation." Recognizing the criticality of well kick volume, or kick tolerance, early detection could result in a significant increase in drilling operation safety and efficiency. Orban et al6 stated that "The danger of undetected influxes grows with the increase of average well depth, drilling through deep water and the tendency to drill with lighter mud. The detection of influx is still commonly based on unreliable and/or inaccurate methods." However, using a closed-loop system and accurate flow measurements brings the possibility and potential for early gas kick detection in OBM before the gas has time to go into solution. In addition, coupling early detection with a computer controlled hydraulic choke, the MFC method minimizes the total volume of gas in the wellbore.

Automated Kick Control Procedure for an Influx in Managed Pressure Drilling Operations

“…The duration for this condition will be based on the confirmation that the influx has ceased to flow and experience. This phase is similar to the Micro-flux control method by Santos et al (2003) and Santos et al (2007). At the same time, the flow rates through the mud pump and backpressure pump are maintained at the initial values.…”

“…Dynamic well control during MPD has been of interest in the literature for many years. Santos et al (2003) and Santos et al (2007) presented a Micro-flux control method, which is the monitoring and adjustment of return flow to control influx during drilling operations. The alternative initial responses to kicks during MPD were explored in Bacon et al (2012); Davoudi et al (2011);Smith and Patel (2012), by increasing casing pressure until flow out equals flow in.…”

The Estimated Formation Pressure During Drilling Operations, in Drilling Wells, and an Exploration of Steps towards Efficient Drilling

“…After determining the mathematical relationships for the estimation of the formation pressure by an adaptive observer, the results provided from the adaptive observer and estimator are simulated to real data, and the acquired data are analyzed. [7] , [8] , [9] , [10]…”