Safety And Assessment Method And Software Design For Casing Program

Casing Program is an important factor to affect the safety of well drilling, well completion and production of oil and gas. Reasonablity and security of casing program is the key factor for drilling and completion. The design of casing program is the basic design of drilling engineering, and it is linked to the overall efficiency of drilling engineering. Reasonal casing program is not only favour of drilling safely and extending mining life, but also dramatically reducing the cost of drilling. Especially for underground pressure information with uncertainty, according to three pressure profiles, a lithologic profile and six design coefficients, it is hard to meet with reasonablity and security of casing program.This paper fully absorbed and took note of reserch achievements of scholars at home and abroad., respectively and particularly analyzed the five factors (geological sealing point,well lose,well kick, well collapse, sticking)which affected the safety of casing program, introduced the quantitative calculation models of them. Using mathematical statistics approach, the author especially research the probability of well lose,well kick, well collapse, sticking on condition that the formation pressure was uncertain. Triangle distribution was used to calculate the probabilty of the four accidents when the data of formation pressure was rare in the early stage of oil field exploration and exploitation, then determined the fuzzy membership functions. Normal distribution (guassian distribution) was used when the data was abundant in the later period of oilfield development, then determined the fuzzy membership functions. In order to response the reality of engneering objectively and accurately, analytical hierarchy process (AHP) was applied for weight coefficient of the the four accidents. The result of multiplying weight coefficient by fuzzy record of degrees is the comprehensive risk probability of casing program, and then tentatively divided the safety of downhole into four levels (security, normal, dangerous, very dangerous) on the base of expert experience and well site requirement. Therefore, the author put forward a new kind of method of casing program safety assessment methods which transforms the quantitative analysis and caculation into qualitative judgment and determination.The author put forward "safety drilling fluid equivalent density window" based on fuzzy membership, and illustrate its expression method and determination method. The author preliminarily forecast the effect on design of casing program, and what the author did was conducive to design casing program from a new view on condition that the formation pressure was uncertain.According to the theory above, the author adopted Visual Studio2010development platform and SQLserver2000data platform to develop a software named "Safety Evaluation of Casing Program" with C#.Net programming language. This paper particularly introduced the process flow diagram and other application methods of this sofeware. This software was used to evaluate the safety of casing program in a exploratory well of Tarim Oilfield, the result was consistent with engineering practice.All in all, the results of this paper can contribute to evaluate, prevent, monitor down-hole accidents, and also analyse cause of accidents and determine the accident layer with necessary and accurate data.