Understanding Kick Tolerance and Its Significance in Drilling Planning and Execution
- K.P. Redmann Jr. (Chevron U.S.A. Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- December 1991
- Document Type
- Journal Paper
- 245 - 249
- 1991. Society of Petroleum Engineers
- 1.14.1 Casing Design, 1.1 Well Planning, 1.6.10 Running and Setting Casing, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.2.1 Wellbore integrity, 1.10 Drilling Equipment, 1.6 Drilling Operations, 1.7.5 Well Control, 5.3.2 Multiphase Flow, 6.1.5 Human Resources, Competence and Training, 1.11 Drilling Fluids and Materials
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Kick tolerance is a drilling parameter that has prompted both confusion and misunderstanding in the drilling industry, yet its importance to drilling engineers may be increasing exponentially. The increasing number of worldwide drilling catastrophes may spur government agencies to tighten controls on casing-setting-depth criteria, requiring pipe to be set once minimal kick tolerance values are reached. A thorough understanding of kick tolerance is necessary in both drilling operations and casing program design. Confusion involving kick tolerance may be attributed to the concept of zero gain, which is commonly referred to in many accepted definitions of kick tolerance. This paper presents an innovative approach to determining true kick tolerance that not only incorporates the conditions of an influx within the wellbore but also considers the possible reductions in kick tolerance caused by the circulation of that influx from the wellbore. New techniques are available for hand-held calculators, which are now more accurate in determining influx pressure and volume anywhere within the wellbore, A typical well example with illustrations describes kick tolerance and emphasizes the influence of other drilling parameters. Integration of kick-tolerance considerations into the well planning process also is demonstrated.
The concept of kick tolerance has been controversial in the drilling industry. Many say it fosters a false sense of security. Much confusion can be credited to the term "zero gain," which is used in this commonly accepted definition: kick tolerance is the maximum increase in mud weight allowed by the pressure integrity test of the casing shoe with no influx (zero gain) in the wellbore. To the drilling hand on the rig, this means, "How much I can weight up to kill the well without breaking down the shoe, assuming zero pit gain?" All too often, the zero-gain condition is either misunderstood or omitted entirely.
Previously published papers have defined kick tolerance in terms of a particular field or operation, developing equations that include safety factors, trip margins, and pit gains common to that environment. Although interesting and discernible to the drilling engineer this may add to the confusion of the average field drilling hand. In addition, governmental regulations may lead to further misunderstanding when improperly interpreted. Minerals Management Service 250.54(a)(6) states, "A safe margin, as approved by the District Supervisor, shall be maintained between the mud weight in use and the equivalent mud weight at the casing shoe as determined in the pressure integrity test."
Although each well should be considered individually in the de-termination of such a safe margin, many contend that the futurwill see a standard value for this parameter defined as 0.5 lbm/gal. This requirement could mislead many drillers into believing that they can continue to drill until the mud weight equals exactly 0.5 lbm/gal less than their shoe test.
For a better understanding of kick tolerance, the derivation of the kick tolerance equation, based on the above definition, is presented. This equation encompasses the effects of an influx in the presented. This equation encompasses the effects of an influx in the well-bore at initial shut-in conditions. And, of course, no examination of kick tolerance would be complete without consideration of the effects as the influx is circulated from the wellbore.
It is likely that government regulatory agencies may soon dictate not only a minimum value for kick tolerance, but also the method of determining that value. A thorough understanding of kick tolerance and how to calculate it while drilling are very important for the drilling representative at the rigsite.
The drilling engineer in the office also must consider kick tolerance during the well design. Pore pressure and fracture gradient information, if available, are excellent when used effectively to select casing setting points. However, kick tolerance must also be incorporated, especially in the case of long, openhole sections. Other factors, such as hole stability, may require an increase in mud weight. Should this occur, the minimum allowable kick tolerance may be experienced earlier than anticipated, and governmental regulations may require casing setting.
Studies have shown an increase in the number of blowouts worldwide, resulting in escalating costs and increasing liability. The drilling program may soon come under close scrutiny by the various government agencies, which win undoubtedly set stricter guidelines for the drilling of all wells, possibly including kick tolerance.
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