Predicting and analyzing sustained casing pressure while taking into consideration the gas dissolution effect

Cement sheath failure is one of the important reasons for the generation of sustained casing pressure (SCP) and it seriously threatens the safety production of oil and gas wells. Based on the gas flow equation, the SCP prediction model considering gas dissolution was established by using the composite cement sheath permeability to characterize the failure degree of cement sheath. The comparison between the calculation results and the field measurement data show that this newly established model has higher prediction accuracy. By taking the gas dissolution into consideration, the gas leakage in the annulus can be predicted accurately. Dissolution effect has an important influence on the early pressure building up process, and with the increase of the dissolubility, the prediction error increases, so increasing the amount of pressure testing data appropriately is beneficial to reduce the prediction error. The SCP prediction model considering gas dissolution was used to predict the SCP in the Lingshui Gasfield. It is indicated that with the increase of the composite cement sheath permeability, the rising speed of the sustained casing annulus pressure increases obviously. The reduction of the annulus fluid density can lead to the increase of the maximum sustained annulus pressure. Presetting the annulus volume can slow down the increase of the annulus pressure. From the view point of engineering, ensuring cement sheath integrity in the whole service life of gas well and taking into consideration the effect of drilling fluid settlement are of great significance to annulus pressure management.