Directional wells and cluster wells have become a conventional drilling technique now, which is widely used in various types of oil and gas reservoirs. Each year, more than half of the total drilling are directional wells in China. The main work is not to aim the target area, but to track the reservoirs now. Geosteering drilling is an important technical approach to improve single-well production and recovery ratio, to achieve the “less wells more production” idea. China Geosteering Drilling System (CGDS), integrated the technology of drilling with logging and reservoir engineering, applies the near-bit geological and engineering parameters as well as controlling method to ensure that the wellhole trajectory can pass through reservoir and get best location while drilling. The wellhole trajectory can be adjusted and controlled timely according to the formation features measured by CGDS. The drilling bit is equipped with “eyes”, which can identify oil/gas layer during drilling. Since 2011, we have provided CGDS geosteering services in 29 horizontal wells in Songliao Basin. The total footage reached 18255m, and the longest footage in horizontal section was 1325m in single well, while the average sand penetration rate is above 85%. Comparing with the horizontal wells operated by conventional LWD tools in the same block, the results of the field application shows that the CGDS geosteering system can significantly improve sand penetration rate and substantially reduce the drilling duration. On the basis of introduction to the system, this paper focuses on comparative analysis of significant application effect of CGDS geosteering system for the heterogeneous reservoir in Putaohua Area of Songliao Basin, as well as the lessons learned. Helpful case histories will also be presented.

Combined with other measurements, neutron porosity tool provide basic and important parameters for real-time formation evaluation and geosteering. In earlier neutron porosity LWD systems, the porosity instruments containe an isotopic chemical source which emit fast neutrons. Using the chemical neutron source, it should be meeting the problem of handing, shipment, and storage. For radiation safety consideration, non-chemical source based neutron instruments will be the best choice for measurement while-drilling. A new type of non-chemical source based neutron porosity instrument has been developed and prototyped. The instrument was designed for porosity measurement while-drilling. it consists basically of an accelerator neutron source and several neutron detectors. The accelerator based neutron generator source can be switched on and off by electronic circuit and software control. The development of new porosity instrument includes two parts - method study and tool design. In method studies, computer modeling was use to tool structure designs and detector parameter choices. Both computer modeling and experimental measurements made in standard formation were used to determine the tool responses. The field test has been made with two prototype tools. Comparing the measured porosity data with wire-line neutron logging data, they are in good agreement. The preliminary test and data analysis show that the designed tools have many new features over chemical source based neutron porosity tools. This paper will highlight the technical development and present helpful case histories and recommendations.