Squeeze cementing has been a common oil field operation for decades. During this time, technical improvements in squeeze job performance have been achieved through (1) a better understanding of hydraulic fracturing principles, and (2) utilization of fluid loss additives. In spite of these improvements, however, the common practice of interpreting downhole performance from surface pressure indications has remained arbitrary and imprecise. Typically, attainment of some specified final surface pressure is regarded as an indication that the well has been squeezed, with little or no regard for fracture gradient, frictional pressure, or hydrostatic pressure---all of which contribute to the actual downhole squeeze pressure.
Computerized simulation of squeeze cementing operations, which allows operators to take into account various well parameters, has recently been developed. Based on fluid densities and rheologies, fracture gradients, and well configuration, a prediction of nonsqueeze surface pressure is provided for the entire job. This allows operators to obtain an accurate determination of when they are actually getting a squeeze--without excessively exceeding the fracture gradient--by noting when actual surface pressure rises significantly above the predicted pressure.
The simulator has proven particularly useful in squeeze job applications utilizing foam cement. A description of operation of the simulator is provided, including case histories comparing actual and predicted wellhead pressures.