Well Integrity as a Fundamental Precondition for a Safe Oil and Gas Production - A Practical Approach from the Drilling Engineering

The principles and procedures to achieve a long term well integrity belong to one of the main topics in the oil and gas industry as it is one of the main key challenges as well. There are many quite specific and often relatively theoretical papers available, but the question is how to deal with such a complex topic practically. The following steps and analysis for a comprehensive well integrity assessment seem to be adequate in terms of drilling engineering as other disciplines (completion, production) are not considered here: Analysis of the fresh water aquifers, the pressure regime and the geology Definition of the sensitive formations as basis for scenario assessments. Adequate casing design in regard to corrosion inhibition and the load cases expected during the lifetime of the well. Risk assessment in case of a high mud weight difference before and after the cementation. Analysis of the cement distribution and mud displacement, respectively. Therefore, simulations and the real pressure curves are compared. Conducting pressure tests on casing, liner packer and annulus cement to test directly the tightness of the well during the drilling phase. Logging and assessment of CBL/VDL (Cement Bond Log/Variable Density Log) and caliper logs as indirect measurements. The challenge of a well integrity assessment is the interpretation of the available data. This needs to be done by considering the geology with its specific attributes (fluid composition, pressure etc.) and the sensitive formations at all times. This is one of the preconditions for a comprehensive assessment and reliable conclusions. Nowadays, well integrity can be assessed by using adequate processes, logging and pressure tests. Nevertheless, the main challenge is the interpretation of the data and the decision making in case of deviations.