American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
Abstract In blowout control and prevention planning, the prime detection instrument needs to planning, the prime detection instrument needs to be designated and its minimum sensitivity specified. Sensitivity requirements will depend on the drilling environment, i.e., casing depth, reservoir properties, mud underbalance possibilities, rig reaction time, circulating rate, etc. Through use of a computer program (KIKSIM) that quantifies the transient characteristics of hydrocarbon gas in the annulus of a drilling well, comparisons are made of detection instrument alternatives.
Introduction In an earlier paper, the computer program KIKSIM was used to illustrate how program KIKSIM was used to illustrate how changes in mud circulation rate can aid in well control. The KIKSIM program which develops information concerning the transient characteristics of hydrocarbon gases in the annulus of a kicking well also has considerable value in planning. Among the planning decisions that can be improved with KIKSIM are selection and establishing specifications for mud flow sensors and pit level recorders. The concept of warning time is introduced and stressed.
This report deals with the detection of gas in the annulus in drilling ahead situations. It does not deal with detection of formation fluids during trips which is a distinctively different problem.
DETECTION STAGES In drilling ahead situations formation gas in the borehole can be detected and measured at three stages, which we will refer to as the entry, mud transport and "expansion burst" stages.
Obviously it is to our advantage to try to detect gas as soon as possible, e.g., as it enters the borehole. Since we may at times be dealing with relatively small volumes at bottomhole conditions, this may not always be possible.
The second stage during which we may detect gas is during mud transport of the gas up the hole. As mud transports gas up the hole it slowly expands and this expansion can be used to detect gas. The mud transport stage is arbitrarily defined as that period during which the rate of gas ascent is largely (2/3) determined by the mud circulation rate.