Study Of Wellbore Stability&Reservoir Protection In G Block Of Gabon

The G Block in Gabon is located northeast of the Port Gentil of the Ogooue province. Itis an important exploration and development block of Sinopec Overseas. Most of the drilledwells are exploratory wells. For the complex geological conditions, many technical problemsrelated to wellbore stability and reservoir protection were encountered during the drillingprocess, such as well leakage, collapse, severe gas invasion and other wellbore instabilityproblems not only seriously affected the efficiency of drilling and downhole safety, but alsoseriously affected the progress and overall exploration and development effectiveness.From the drilling geology, engineering, wireline logging, mud logging, cementing, welltest data analysis and study, the reservoir lithology, geological features have been known.There exist wellbore stability and reservoir protection aspects of technical difficulties andproblems. Wellbore instability caused by the collapse, lost circulation, kicks, and the resultingpoor cementing quality etc.Comprehensive analysis of wellbore stability mechanism of G block was done toidentify the main factors for wellbore instability. The main reasons for the wellbore instabilitywere found and some technical countermeasures were proposed. Drilling fluid system andadtives are preferable."Shield blocking technique to maintain wellbore stability" is carriedout by particle size analysis and formed to deal with G block complex formation wellborestability. A set of theory and methods to maintain the wellbore stability has been formed andconducted in well G-9, G-10, received very good results, avoided the emergence of wellboreinstability, safeguarded the wellbore stability during drilling; Form a well leakage preventionand treatment programs and protect the downhole safety and cementing quality. Acceleratethe speed of drilling and the development process of G block.Comprehensive analysis of the reservoir protection of G block through porosity,permeability testing, X-ray diffraction experiments, as well as core-sensitive experiments,carried out in G block and damage mechanism of reservoir, to find the main reasons for thepollution of G block reservoir, proposed the main technical measures to protect G blockreservoir, drilling fluid system is preferable, well G-11application shows that the effect isobvious. The whole process of using underbalanced and managed pressure drillingtechnology to protect the reservoir was suggested.