No abstract

Shallow drilling hazards present a significant risk to the health, safety, and environment of upstream oil and gas operations. Shallow marine formations are often near the critical porosity limit, where the sediment is very poorly sorted, mechanically weak and often unconsolidated. As the sediment begins to compact, well-construction challenges are created as formation stresses and fluid pressure changes, usually resulting in the operator having to set extra casing strings near the surface. The United States Department of the Interior, Minerals Management Service (MMS) requires the use of a diverter and a conductor string of casing if there is any possibility of a shallow hazard in the area of a proposed well. Proving shallow hazards do not exist in the area requires resistivity and porosity logs approved by the MMS. This operator requested these logs be run in 22 and 17 ½ in. boreholes using Logging While Drilling (LWD) technology as no wireline logging was planned. In large hole sizes, the porosity log is generally the limiting factor for most wireline and LWD technologies, with nuclear measurements from most vendors designed for hole sizes no bigger than 12 ¼ in. LWD Acoustic measurements in this well provided acceptable determination of porosity in borehole sizes up to 22 inches in extremely slow formations.The objective of this application was to acquire an LWD acoustic compressional slowness log below the drive pipe. Modeling shows and supports the ability to measure in this demanding environment where the compressional slowness often approaches that of the drilling mud. A 9 ½ in. LWD acoustic device was optimized for shallow data acquisition for the large borehole size and very slow acoustic velocities anticipated. While drilling, real-time LWD logs showed conclusive evidence of the absence of hazards and were immediately accepted by the MMS for the waiver. This paper validates the feasibility of using LWD logs to gain a conductor waiver from the MMS. Benefits include reduced operating costs associated with a wireline program and the savings involved in removing the conductor string from the casing program. On this multi-well batch drilling project operational savings of about 2.15 million USD were realized.

Borehole imaging is a useful and well-known formation evaluation technology. In recent years, two major developments have opened the door to several new application areas. First, the technology to acquire borehole images was conveyed from pure wireline systems to logging-while-drilling systems. Imaging-while-drilling technology benefits from acquiring borehole images from a nearly unaltered borehole in an almost virgin formation. Secondly, high-end mud pulse telemetry systems, in combination with advanced data-compression methods, enable the reception and use of high-resolution borehole images while drilling. This data is available for further real-time analysis at the surface during different stages of the wellbore construction process. Several examples going beyond the pure formation evaluation aspect, demonstrate how high-resolution borehole images are used to improve wellbore construction. In particular, methods with respect to wellbore integrity, geosteering, and completion stage identification are demonstrated. These applications use the high resolution borehole images to identify borehole events such as induced fractures or breakouts, as well as formation features such as bedding, faults, or natural fractures. Wellbore integrity methods mainly use the images to identify borehole breakouts and induced fractures. Geosteering is predominantly based on the evaluation of bedding at a dipping angle with respect to the borehole that can be determined from images. The completion stage of operations benefits from the identification of natural fractures and fractures that were created during hydraulic stimulation of offset wells. TX 75083-3836, U.S.A., fax +1-972-952-9435

Shallow drilling hazards present a significant risk to the health, safety, and environment of upstream oil and gas operations. Shallow marine formations are often near the critical porosity limit, where the sediment is very poorly sorted, mechanically weak and often unconsolidated. As the sediment begins to compact, well-construction challenges are created as formation stresses and fluid pressure changes, usually resulting in the operator having to set extra casing strings near the surface. The United States Department of the Interior, Minerals Management Service (MMS) requires the use of a diverter and a conductor string of casing if there is any possibility of a shallow hazard in the area of a proposed well. Proving shallow hazards do not exist in the area requires resistivity and porosity logs approved by the MMS. This operator requested these logs be run in 22 and 17 ½ in. boreholes using Logging While Drilling (LWD) technology as no wireline logging was planned. In large hole sizes, the porosity log is generally the limiting factor for most wireline and LWD technologies, with nuclear measurements from most vendors designed for hole sizes no bigger than 12 ¼ in. LWD Acoustic measurements in this well provided acceptable determination of porosity in borehole sizes up to 22 inches in extremely slow formations.The objective of this application was to acquire an LWD acoustic compressional slowness log below the drive pipe. Modeling shows and supports the ability to measure in this demanding environment where the compressional slowness often approaches that of the drilling mud. A 9 ½ in. LWD acoustic device was optimized for shallow data acquisition for the large borehole size and very slow acoustic velocities anticipated. While drilling, real-time LWD logs showed conclusive evidence of the absence of hazards and were immediately accepted by the MMS for the waiver. This paper validates the feasibility of using LWD logs to gain a conductor waiver from the MMS. Benefits include reduced operating costs associated with a wireline program and the savings involved in removing the conductor string from the casing program. On this multi-well batch drilling project operational savings of about 2.15 million USD were realized.

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