A new high-efficiency logging system from Baker Atlas, FOCUS, made its public debut at the Canadian Society of Petroleum Geologists (CSPG) convention in June 2003. Since then, the six units based in Brooks, Red Deer, Grand Prairie and Lloydminster have been deployed all over the Western Canada sedimentary basin region.

System mechanics

The logging system consists of the four primary openhole services: resistivity, density, neutron and acoustic measurements, plus auxiliary services. Some of the real-time deliverables include logs and plots to help users improve their formation evaluation efficiency. These include real-time 1-D radial inversion processing of array resistivity data to produce more accurate measurements of the resistivity of the flushed zone (Rxo) and true resistivity (Rt). The value of the array resistivity high definition induction log (HDIL) is enhanced by its ability to produce 1-ft (.3-m) vertical resolution data, which is ideally suited for evaluating hydrocarbon saturations in many of the thinly bedded formations common in Western Canada.

Design changes to the nuclear porosity logs, including improved detector response, allow high logging speeds, which increase efficiency when compared to conventional instruments and enable the production of a real-time nuclear porosity cross-plot log. Auxiliary measurements include the correlation gamma ray, borehole temperature, downhole tension, mud resistivity, borehole deviation and a two-arm Y-axis caliper. Downhole tension and accelerometer measurements help verify the validity of the data and allow it to be corrected for "stick and pull." These corrections improve the accuracy of the log data recorded under adverse borehole conditions. Temperature data and an accurate cement volume output are useful for future completion plans.

Data flow and delivery are additional key components that add another dimension of efficiency to the system. Data flows between the logging instruments and Baker's data delivery centers via a satellite communications system linked directly to the Baker Atlas WellLink Web-based delivery system. The log data typically is uploaded within minutes of finishing the data acquisition segment of the logging operation and can immediately be viewed by clients using any computer connected to the Internet. This provides clients with 24 hours of secured access to their data from anywhere in the world.

Specifications and design criteria

A critical component to consistent high-efficiency wellsite operations lies in the improved design of the downhole logging tools. All sensors have been designed to provide accurate measurements at a standard logging speed of 60 ft/minute (18.3 m/minute). The logging tool string is shorter and lighter than conventional tool strings. This design feature is intended to promote and maximize wellsite efficiency. The tools also are easier for the wellsite crews to handle, enabling faster rig up and rig down and reducing the total rig time needed for a logging operation. The shorter instrument design reduces overhole (rathole) requirements by as much as 50%, saving rig time needed to prepare the well bore for logging. All measurements can be corrected for stick and pull, which has a much larger effect on logging measurements at higher logging speeds. The result is data accuracy and precision at the higher speed that is equal, and in many cases superior, to that of conventional logging.

Value drivers

There are two key efficiency attributes that make the product an attractive proposition. The first attribute is the short instrument string length. The highest sensor measure point is at 32 ft (9.7 m) for the gamma ray instrument, meaning overhole requirements to accommodate the tool string are minimized. Current regulations in Alberta often limit the amount of overhole to 50 ft (15.25 m) below the depth specified on the well license, so this attribute can be significant. From an efficiency perspective, drilling time for overhole is reduced, and the logging can be completed in a single trip rather than splitting up sensors into multiple trips to ensure logging data from each instrument is recorded in the zone of interest. Additionally, there is timesavings from the faster logging speeds at which the tools are capable of recording data. The recommended logging speed of 60 ft/minute (18.3 m/minute) significantly reduces logging times compared to other logging systems that require speeds of not more than 30 ft/minute (9.15 m/minute).

Additions to original service

In June 2003, the initial offering from the system was limited to traditional triple and quad combos (resistivity, density, neutron, acoustic services). However, soon after the introduction, tandem Z-densilog capability (Tandem ZDL) was added to accommodate logging in boreholes where borehole breakout is severe enough to compromise conventional density tool measurements. When breakout occurs it can be difficult, sometimes impossible, to get valid density readings. The Tandem ZDL takes two density measurements, aligned 90° to each other, to ensure at least one set of density measurements is taken in the short axis of the elliptically shaped borehole.

In addition, two caliper devices are normally deployed on the tool string to measure the diameter and volume of the well bore to accurately determine the cement volume requirements. Cement volume calculations can be adversely affected if only a single-axis borehole diameter measurement is made and borehole breakout is occurring. Therefore, it is always best to make two borehole diameter measurements with the caliper tools offset by 90° to ensure accurate borehole geometry information is gathered. A MiniLog shallow depth-of-investigation micro-resistivity device, for permeability and fracture indication, completes the measurement suite.

An additional pressure testing service, the formation multi-tester (FMT), is also available to compliment the standard quad- or triple-combo data set. The FMT is run on a separate trip after the quad- or triple-combo data is acquired.