A New Method to Evaluate Leak-Off Tests in Shallow Marine Sediments (SMS)

Abstract

Abstract Leak-off Tests (LOT) and Pressure Integrity Tests (PIT), are verification methods to evaluate cement jobs and estimate the formation fracture pressure at the casing shoe. Although analysis of LOT in deep wells is considered a well known and practical procedure, the interpretation of LOT in Shallow Marine Sediments (SMS) is less clear. LOT in SMS gives a non-linear relationship between the pumped volume and the observed pump pressure and there is no obvious point of deflection or "leak off’ from the initial linear section of the plot. Because of non-linearity of LOT plots in SMS, LOT could be inconclusive and difficult to interpret. Incorrect interpretation of LOT would lead to costly problems that might jeopardize well progress such as; unnecessary squeeze jobs, premature setting of casing, and lost circulation problems. This paper presents a new method to analyze casing shoe leak-off pressure in the SMS. A mathematical model is derived to assist in analyzing non-linear LOT behavior and the new method is supported by field data from LOT in SMS. LOT interpretation is the basis for the critical drilling decisions such as; casing setting depths, cement job evaluation, drilling fluid selections, and well control methods. Correct interpretation of the LOT can help to avoid variety of problems and save considerable amount of time and money.