When Halliburton introduced the InSite ADR azimuthal deep resistivity sensor in 2008, oil and gas operators were increasingly focused on recovering reserves from complex reservoir structures. With characteristics such as relatively thin target zones, complex fault-block structures, steeply dipping beds, pinch-outs, and lenses, these reservoirs require accurate positioning of wells within tight targets. The InSite ADR sensor offers control in the guidance of horizontal wells through the reservoir by measuring the resistivity of the formations around the tool. The technology won the formation evaluation category of Hart Energy’s 2008 Meritorious Awards for Engineering Innovation.

During that time, the industry had been advancing the geosteering technique, which uses real-time responses from LWD sensors in the drilling assembly to determine the position of the well within the geological structure. Drilling tools such as rotary steerable systems and conventional steerable motors are then used to keep the well trajectory in contact with the reservoir.

Conventional resistivity sensors could detect bed boundaries or fluid contacts several feet away from the horizontal path. “These techniques were reliable in relatively simple structures where the well was steered relative to a single, well-defined boundary, but in thin or complex reservoirs, these tools were not able to distinguish, for example, between shale beds above and below the well path,” Tim Parker, product manager of LWD for Halliburton’s Sperry Drilling services, said.

Compared to previous LWD resistivity tool designs, the InSite ADR brought improvements in resistivity measurement quality. It also brought two advantages for geosteering applications, including the introduction of azimuthal sensitivity and deep-reading geosignals in addition to the resistivity measurements. With azimuthal sensitivity, the volume of the measurements is biased toward one side of the tool. By rotating and scanning 360° around the wellbore, the tool can create a 3-D resistivity map of the surrounding formation. “It is now possible to determine whether a particular tool response was due to a boundary above or below the wellbore, allowing for much better decision-making in steering the well,” Parker said.

Derived from the electromagnetic signals from the tool’s transmitters, geosignal sensitivity extends further from the wellbore than that of resistivity measurements. This increases the range in which boundaries can be detected. “The geosignals are also azimuthally sensitive, and it is these which allow us to calculate the distance as well as the direction to boundaries up to 18 ft [5 m] from the wellbore,” Parker said. “The combination of azimuthal sensitivity with deep-reading measurements provided a much more detailed picture of the surrounding reservoir than had previously been possible. This, in turn, allowed more precise positioning of the wellbore, greater exposure to the productive zone of the reservoir, and ultimately increased production.”

The tool has been used in more than 3,000 runs since its introduction and has logged more than 1,700 km (1,060 miles) of borehole in 35 countries. In the Eagle Ford shale in Mexico an operator used the tool to geosteer a well for a total of 2,374 m (7,789 ft), including the landing interval and the lateral production interval of 1,311 m (4,300 ft) within a gas production zone that was 3 m (10 ft) thick. “The improved confidence associated with the wellbore position allowed the well to be drilled quickly, cutting the planned drilling time by more than half and saving 12 days rig time,” Parker said.

The company continues to improve the service, primarily through enhancement of the interpretation software rather than the physical tool design. “We now have a much more sophisticated set of algorithms than we did in 2008, establishing more accurate and complex interpretations of the data acquired by the tool,” Parker said.

The InSite ADR sensor remains the company’s primary geosteering service, with shallow-reading, high-resolution borehole imaging tools often used to complement the technology. The company is developing tools that can operate in harsher environments and provide more detailed information about the reservoir structure around the wellbore.