Application of leak-off test data in formation fracture gradient correlation for Niger Delta Basin natural gas wells development

Abstract

Abstract Offshore drilling of gas wells in the Niger Delta is becoming very expensive and requires highly skilled manpower. Therefore, it is essential to accurately update the fracture pressure data, maintain adequate measurement while drilling, and ensure acceptable prediction with conventional empirical correlations while drilling operations are ongoing to avoid non-productive time (NPT). To effectively drill an offshore well and deliver it safely while protecting personnel, the environment, and equipment, drillers must ensure that the wellbore pressure is sufficient to balance the pore pressure without exceeding the fracture pressure anywhere along the open section of the well. Calculating and predicting the fracture pressure is critical for reducing NPT in offshore drilling and ensuring the safety of workers and goods on-site. There are numerous relationships for predicting the fracture pressures. However, they are primarily limited to onshore and shallow water fields, and as wells are drilled deeper in the Offshore Niger Delta field, a correlation (equation) based on offshore leak-off test (LOT) data is required to correctly estimate the crack pressure. Thus, this study employs a mathematical modelling technique to create an improved offshore fracture gradient equation from leak-off test data tailored to the needs of the offshore Niger Delta. The generated correlation (equation) was statistically examined, yielding a reliable coefficient of determination. It was tested again with the field cases, and the results were similar to the LOT results.

Keywords

• Natural gas wells
• Leaf-off testing
• Niger Delta
• Offshore drilling
• Mathematical modelling