On this appraisal well, the operator needed optimal reservoir delineation to set up for accurate reserve calculation and future field development. Thus the 9⅝-in casing had to be accurately set 5 m above the top of the target formation to enable complete coverage for the subsequent coring, openhole wireline logging, and well testing program.
What was tried first
When the exploratory well was drilled, conventional correlation and sampling techniques failed to determine the top of the formation. As a result, the conventional BHA drilled completely through the first 20 m of the upper carbonate formation when setting the 9⅝-in casing. This prevented openhole logging and well testing data to optimally delineate the target formation.
Schlumberger proposes look-ahead-while drilling technology
Schlumberger suggested drilling an S-type well using IriSphere service. IriSphere service provides a real-time look ahead of the bit and advanced automated inversion to accurately detect formation features before contact with crucial boundaries. It also detects top of formation at least 10 m ahead of the bit and enables increased ROP and fewer BHA trips out of hole.
IriSphere services pinpoints ideal casing set to optimize well operations
IriSphere service first verified that the conventional indication of top of formation at 1,535-m MD was invalid. Then it enabled normal drilling ROP to 176 m deeper than the previously assumed formation top, avoiding time-wasting conventional spot samples at 5- to 10-m intervals because it also distinguished several thin limestone stringers from the target carbonate. At 1,703-m MD, IriSphere service detected the formation top 10 m ahead of the bit, enabling a 9⅝-in casing to be set at 1,706-m MD, approximately 4–5 m above the top of formation.
IriSphere service enabled placing the well to optimize coring, openhole wireline logging, and a well testing program for accurate reservoir delineation, reserve calculation, and future field development. This confirmed the top of formation at 1,711-m MD. Thus, IriSphere service also avoided drilling an unplanned 6-in hole.