A shale gas play operator in Central China has commenced horizontal well drilling development. Upon completion of multiple vertical pilot or evaluation wells, the shale gas target reservoir zones have been identified and are to be developed with horizontal wells. Due to the difficulties and risks associated with acquiring wireline measurements in horizontal sections, Logging While Drilling (LWD) measurements along with Rotary Steerable Drilling Systems (RSS) are used to provide real time formation evaluation, allow the well to be placed optimally within the target reservoir, reduce drilling risks, improve rate of penetration and help optimize completion design. An integrated LWD tool and RSS was run for the first time in a horizontal shale gas well. The LWD tool delivers elemental spectroscopy, formation sigma and sourceless neutron along with the conventional triple-combo measurements of gamma ray, density, thermal neutron and resistivity. The system provided: Improved lithology determination and enhanced formation grain density evaluation from elemental capture spectroscopy. This led to improved porosity determination and completion design Optimized lateral placement in the best quality sub-layer with near-bit GR and density images The ability to avoid drilling hazards through real-time monitoring of the drilling parameters available from the LWD tool Greatly improved ROP through the improved drilling capabilities of the RSS. This minimized the time that the formation was exposed to drilling fluids before measurements were acquired. These measurements provided the information required for the success of the first horizontal drilling in a shale gas play. This paper will detail the use of LWD measurements and a RSS drilling system for an integrated shale gas solution providing comprehensive petrophysical evaluation, accurate well placement, and drilling efficiency optimization for the first horizontal well drilled in a shale gas play in Central China.

More than 50% of the heavy oil resources for PetroChina Liaohe exist in thin (approximately 3-to 8-m thick) reservoirs. For this type of reservoir, steamflooding with conventional vertical wells is not economically profitable, and in-situ combustion methods are not applied because of operational difficulties. Horizontal well technology brought a new direction to attempts to improve technical and economic performance of steamflood operations. Many experiments had been conducted to use the technology in the Liaohe oil field to achieve economic production, but the expected results were still not achieved. Lessons learnt indicate that the root cause is the poor oil contact of the horizontal wells' trajectories in the thin, heavy oil reservoir. A pilot project was conducted to explore whether horizontal well technology in combination with optimized cyclic steam stimulation could deliver economic production from these thin heavy oil reservoirs. Horizontal well placement was accomplished by using near-bit azimuthal measurements and images.Both the feasibility and economic performance of the technology have been studied in this five-well pilot project. Comparing the performance of these five wells to the previous ones, the results indicate that 1) The well-placement drilling solution can maximize the oil contact up to an average 91% of net-to-gross coverage.2) The well-placement drilling solution improved drilling efficiency by 40%.3) The drilling operation was conducted with no nonproductive time (NPT), compared to the previous NPT maximum of 6 days. 4) The well-placement drilling solution did keep the cost flat, and the cost even slightly declined. 5) The optimized cyclic steam stimulation in well-placement-drilled wells can decrease the cyclic steam stimulation cost over production to 1000 RMB/ton, which is recognized as an economic ideal in the industry. 6) The daily block production has increased from 20 tons/day to 72 tons/day after using the combined wellplacement-drilling and cyclic steam stimulation technology, which is an increase of 210%. 7) The income/input ratios at the end of the fourth year for the two better wells are both 1.48 (reaching a balance at the second and third years, respectively), and ratios for all five wells ratios averaged 0.93, which means the wells will earn net money at the beginning of the fifth year. Compared to the ratio of 0.03 for a previously drilled well, this is not only a big financial improvement, but is also an incentive to revitalize many similar thin heavy oil reservoirs because it proves the possibility of developing them within the economic margin. The success of the pilot project proved to us that horizontal well-placement drilling in combination with optimized cyclic steam stimulation is an effective way to develop thin-layered heavy oil reservoirs within the economic margin in Liaohe oil field. We extended this horizontal well technology to other blocks and have achieved repeated success.

Laminated sand-shale reservoir poses many challenges in formation evaluation and hence risks on decision making such as oil testing or completions, particularly for offshore. This paper presents a new approach of NMR based rock typing, permeability characterization and rapid production prediction for thin sand-shale laminated reservoir, conducted in an offshore field of South China Sea. The method is validated through a study integrating logs, formation tester and drill string test (DST) data, to build a generally applicable approach. It was used for rapid producibility evaluation right after openhole logging, in order to facilitate the decision making of the consequent completion and production test. Based on a quick yet reliable answer, operators can decide whether the well should be completed and where should be tested in order to achieve the lowest cost and HSE impact and better time efficiency for exploration and appraisal.The major challenges facing are: highly laminated sand/shale sequences, strong heterogeneities, complex porosity-permeability relationships, and different scales of different measurements. We set up an improved method using NMR measurements to evaluate effective properties within a depth frame of thin beds in order to overcome the resolution challenge because the individual lamination thickness is about centimeters or even thinner, which is much below the resolution of logs. Comparing with DST results, the accuracy of predicted producibility is in an acceptable range, giving great confidence of the reliability in the study result. This case study has demonstrated the applicability of the new NMR based method, and set up a rapid producibility evaluation approach for thin, sand-shale laminated reservoir; and this new NMR method and the approach applied are not limited to this specific field but applicable to other fields with similar geological settings and formation types in this region.

Formation pressure and mobility measurements play a critical role in the development and management of compartmentalized reservoirs. Conventionally, wireline formation tester (WFT) tool has been used for such appliations. However, reservoir evaluation becomes challenging in high temperature environment, due to the unchangeable temperature limitations of WFT tools.This paper presents a case study where formation pressure and mobility are acquired by applying formation pressure testing while drilling (FPWD) at a high temperature (HT) offshore gas well in South Sea, China. With a thermal gradient of as high as 4.5 degC/100m, the estimated formation temperature is higher than the maximum temperature rating of the wireline tools. By integrating detailed pre-job design maintaining the working temperature at acceptable range and real-time monitoring including data quality control and measurement optimization ensuring the functionality of hardware and the quality of measurement, FPWD has successfully revealed the formation properties.

Located in central China, the Sichuan basin holds the biggest gas reserve in the country. Tight gas reservoir (limestone, dolomite, and tight sand) development has been taking place since early 1992. Since then, relatively thicker gas reservoirs have been commonly developed, and more challenging, very thin reservoirs are now being targeted. Long horizontal drilling combined with multistage hydraulic fracturing is planned. However, the management of the subsurface uncertainties appears as the biggest challenge. Located in a major compressional tectonic area, the geological province presents reverse/thrust faults and high structural dip uncertainty. Lateral property changes in the dolomite target reservoir and a stratigraphic thickness of the reservoir that varies from 1 m to 2 m add to the difficulty. To overcome these challenges and to enhance reservoir understanding, advanced logging-while-drilling acquisition and real-time transmission of high-resolution electrical borehole images, azimuthal gamma ray, and multidepth measurement of formation resistivity were deployed in a recently completed gas well. Based on these data and advanced techniques, structural features including dips, faults, and fractures could be clearly identified in real time while drilling and helped the team to: 1) accurately geosteer the well and significantly reduce the probability of erroneous lateral placement and 2) optimize the completion design and planning of the hydraulic fracturing staging and segmentations. Completed in 2011, the well represents the first successful completion in the thin, tight gas reservoir; a 1095-m horizontal section was drilled with 91% net-to-gross and the gas production was recorded at 123 700 m3/d, exceeding the set production goal of the well by 33%. This particular success is proving that a thin, tight gas reservoir can be profitably developed. Several subsequent wells have been planned to be drilled in different target zones in the Sichuan basin.