openhole

Open-hole refers to a portion of a borehole that has not been lined with casing or cement, allowing direct contact between the formation and drilling or logging tools. Open-hole intervals are common in the early stages of drilling or in appraisal wells and are typically evaluated to determine reservoir properties.

Open-hole logging is used to characterize the formation, including lithology, porosity, permeability, fluid content, and hydrocarbon saturation. Tools are deployed via wireline or through the drill string during drilling (logging-while-drilling) and gather data such as gamma-ray for lithology, resistivity for porosity and oil-water boundaries, density and neutron porosity for porosity, sonic or acoustic velocity for formation stiffness, and borehole imaging to identify fractures and bedding.

After completion, most logging is performed in cased-hole intervals, but open-hole data remains critical for reservoir evaluation and may be used to calibrate later logs. In open-hole completions, sections of the well are left open to production and later perforated; this approach allows multi-zone development but requires careful evaluation and integrity management. Open-hole sections are more susceptible to borehole instability and fluid invasion, and their data can be affected by washouts, mud invasion, and hole geometry.

In the petroleum industry, open-hole data underpin reservoir characterization, well planning, and production optimization, providing a direct view of the formation before casing and cementing alter the interval. The term is also used in discussions of open-hole completions and certain testing methods that take place in uncased borehole sections.