Abstract
The exploitations of deep-water wells often use directional well drilling to reach the target layer. Affected by special environments in deep water, the prediction of pressure loss of cement slurry is particularly important. This paper presents a prediction model of pressure loss suitable for deep-water directional wells. This model takes the complex interaction between the temperature, pressure and hydration kinetics of cement slurry into account. Based on the initial and boundary conditions, the finite difference method is used to discretize and calculate the model to ensure the stability and convergence of the result calculated by this model. Finally, the calculation equation of the model is used to predict the transient temperature and pressure loss of Wells X1 and X2, and a comparison is made between the predicted value and the monitoring data. The comparison results show that the maximum error between the temperature and pressure predicted by the model and the field measured value is within 6%. Thus, this model is of high accuracy and can meet the needs of site construction. It is concluded that this result can provide reliable theoretical guidance for temperature and pressure prediction, as well as the anti-channeling design of HTHP directional wells.
Highlights
In recent years, the focus of oil–gas exploration and development has gradually shifted from shallow-water areas to deep-water areas
During the waiting on cement stage, with the progression of the hydration reaction, the gas will gradually enter the annulus space and cause gas channeling, which occurs when the liquid column pressure is lower than the formation pressure [3,4,5,6]
During the waiting on cement stage, a channeling path is formed by formation fluid entering the annular gap when the annular liquid head is lower than the formation pressure due to the weight loss of cement slurry in the waiting on cement (WOC) stage
Summary
The focus of oil–gas exploration and development has gradually shifted from shallow-water areas to deep-water areas. In the process of weight loss during the WOC stage, the continuous development of static gelling strength leads to insufficient pressure in the cement slurry column to stabilize the formation, which provides a driving force for the annular air channeling [7,8]. Zhang et al [14,15,16] studied the important influence of cement slurry’s stability on weight loss with a large number of weight loss experiments based on the force analysis of cement slurry in the annulus They studied the quantitative relationship between effective slurry column pressure and gas cutting resistance and the factors that affect the former two and set up a calculation model for the process of cement slurry setting, making the condition to cause breakthrough flow in the annulus, which can be used for predicting and evaluating the channeling preventing the ability of cement slurry in the process of setting. Combined with Equation (8), Equation (9) can be expressed as the following difference form:
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