Using LWD Tools during Soil Boring Operation to Identify Offshore Geohazards

Abstract

Logging While Drilling (LWD) tools have been used in most drilling operations whether offshore or onshore, and from top holes all the way to total depth. This practice provides most of the information required for all stake holders of oil and gas reservoirs. The focus of this paper will be the use of LWD tools in soil boring operations which has never been done or recorded before. Site investigation is the first step in gathering geotechnical information for evaluating soil integrity for activities such as pipeline installation, platform construction, jacket installation, or drilling rig positioning. A feasibility study is done by performing a series of in-situ (or lab) tests to help operators and drilling contractors identify any geohazards and prepare suitable mitigation plans. Failure to do so can lead to expensive incidents during subsequent operations such as shallow gas, jackup rig punch through, damage on the jacket, pipeline failures, shallow water flow, gas hydrates, and environmental pollution. LWD tools in combination with standard soil boring investigation (coring, soil sampling, cone penetration test, etc.) provide comprehensive site survey information including rock types, gas identification, wellbore imaging, water saturation, shear measurement, wellbore stability, lithology, and fracture identification. More detailed information can be acquired by using nuclear tools or seismic while drilling but these are not recommended for soil boring operations. In addition, the operator will have continuous formation evaluation data in cases where the surface hole is driven by conductor pipe. (LWD tools cannot acquire data once the casing is set.) Combining petrophysical, geophysical, and geotechnical data at the earliest stage lets operators prevent undesired events by clearly identifying geohazards, and then either mitigating the hazards or determining that the location is unsuitable for further operations.