T/CI 009-2023 Quantitative Evaluation Technical Specification for Downhole Engineering Risk in Deep Drilling Operations

Scope

Main technical content: Deep drilling refers to drilling for deep oil and gas wells with a completed drilling depth greater than 4,500 meters. 3.2 Credibility The probability that a parameter falls within a certain range, with values ranging from 0 to 100%. A higher value indicates higher credibility. For example, the credibility of formation pressure refers to the probability that the predicted formation pressure falls within a specified range, and the credibility of the safe drilling fluid density window represents the probability of safe operation within that window. 3.3 Formation pressure with credibility The formation pore pressure, formation fracture pressure, and formation collapse pressure (commonly called the three formation pressures) profiles are one of the important bases for the design of drilling engineering solutions. However, due to the complexity of geological conditions in deep wells, the incompleteness of interpretation data, and the accuracy of mathematical models, errors in formation pressure prediction are objective. Therefore, the prediction results of formation pressure have varying degrees of uncertainty, and its true value is difficult to accurately predict. The concept of formation pressure with credibility quantitatively characterizes the uncertainty of formation pressure prediction, and the result is not a single deterministic value, but a credibility distribution range, which helps engineers better understand the formation conditions and is also the basis for subsequent quantitative risk evaluation. 3.4 Safe drilling fluid density window with credibility This is an upgrade of the conventional safe drilling fluid density window. By adjusting the credibility (see 5.2), the quantitative control of the safety of the safe drilling fluid density window is achieved. On the basis of the formation pressure profile with credibility, according to the design coefficients in the design method of wellbore structure (reference SY/T 5431-20

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