During fracturing operations, the assessment of downhole conditions could only be based on changes in operating pressure. However, numerous factors influence operating pressure, including the cross-linking status of the fluid, changes in the flow rate of the pumping vehicle, the balance between the friction of the sand-mixing fluid and the column pressure, and the filling of fractures and fluid loss within the formation. These factors collectively determine the development of operating pressure. Given the rapid pace of fracturing operations, it is essential to promptly and accurately assess changes in operating pressure and promptly implement appropriate countermeasures.
1. When pressure changes occur during fracturing operations, the first step is to promptly determine whether the changes are caused by surface equipment, such as variations in pump truck flow rate, sand mixing truck fluid supply conditions, or changes in liquid nitrogen pump flow rate. Second, immediately inspect the fluid cross-linking status and, in conjunction with the stage pumping fluid volume and sand concentration, determine the trend of fluid friction changes. Only pressure changes that occur after entering the formation can effectively reflect the conditions within the formation.
The difference between formation pressure and surface pressure is clearly demonstrated in continuous tubing-driven fracturing operations. For example, in the construction curve of well J72P9H shown in the figure below, the casing pressure fluctuates frequently with changes in the construction flow rate, sand injection stage, and liquid nitrogen injection flow rate, while the stable oil pressure at this time can clearly reflect the formation conditions.
