【系列专题】页岩油气隐形手：储层表征破解油藏密码（2）

With the wealth of data available in the shale plays, modeling is playing a larger role. Companies are able to use advanced computer mathematics to provide production forecasts within seismic datasets.

Logging tools are also getting a new look. Cased-hole logging helps operators find bypassed pay and identify refracture candidates while providing definitive oil and gas saturation information. And logging simulation is using MWD and LWD data to simulate openhole logs in horizontal sections.

Industry adoption of these new techniques will result in more efficient shale development and greater recovery.

The following is a sampling of new technologies and products for reservoir characterization.

BRIDGING THE GAP BETWEEN GEOSCIENCE AND ENGINEERING

Ikon Science leverages geoscience technology to characterize unconventional resource plays ahead of the drillbit and optimize development strategies. Ikon has integrated several key technologies including seismic inversion, rock physics and geomechanical analysis. Recently in the Permian Basin the Ikon team successfully predicted fracture initiation pressure from seismic and validated those predictions using drilling-induced fracture observations in borehole image logs. Ikon’s main seismic technology is joint impedance and facies inversion (Ji-Fi), developed in collaboration with CSIRO. It also is working with industry leaders in rock physics, including Lev Vernik, to develop tools explicitly for characterizing unconventional resources. Ikon’s technologies are focused on bridging a gap between geoscience and engineering, answering direct questions about well placement and completion design. Seismic data provide an important source of spatial information. Physical rock property information can be extracted from the seismic data that can be used as input for geomechanical models. By understanding the stress regime and rock properties, geomechanical behavior of the rock at prospective drilling locations can be predicted. Furthermore, the 2017 alliance between Ikon Science and FairfieldNodal will provide a combination of amplitude vs. offset (AVO)-compliant seismic imaging and quantitative interpretation technology that will undoubtedly lead to some interesting results for shales.

SYNTHETIC SERVICE REDUCES COSTS

Quantico Energy Solutions has developed a synthetic logging service that reduces the cost and risk of obtaining openhole logs. Rather than running LWD, pump-down or tractored tools, the drilling dynamics and MWD gamma can be used to simulate neutron, density and sonic logs with the same accuracy as conventional logging tools. With openhole horizontal logs typically costing 10 times that of vertical logs, horizontal logging is impractical for most operators. Quantico’s logs provide rock property information along the horizontal well at a similar cost to logging vertical wells. Operators can use the horizontal properties to enhance their existing geological models. A case study demonstrated that a typical horizontal well has 20 to 40 times more calibration data in a landing zone than a vertical well. Incorporating derived properties such as rock mechanics or permeability creates significantly more detailed shale models to better target production sweet spots. Mapping compressive strength can significantly improve drilling efficiencies. The order of magnitude increase in well-to-seismic calibration points provides more stable wavelets for seismic inversions and thus greater resolution. Quantico’s process also quantifies velocity and layer-specific anisotropy across a region, leading to the elimination of up to half of the velocity iterations, which can reduce processing time by several months for depth migrations.

NEW PRODUCTION FORECAST DATABASE INCLUDES ALL ACTIVE SHALE WELLS

The TGS Production Forecast Database is a library of every well in the U.S., containing both a monthly production projection and an EUR total. When combined with the Longbow desktop visualization tool, entire EUR basin studies can be built in minutes. This forecast engine leverages the TGS Well Performance Database to create forward production curves for all active producing shale wells derived from historical production data. Curves are generated using hyperbolic fitting, but this model’s advantage includes extended Kalman filter (EKF) techniques incorporated into the process. EKF techniques emphasize the most recent data, identify trends and adjust logic on the fly using a series of matrix math techniques and results in improved efficiency and accuracy. It is the first time to the developers’ knowledge that the EKF theory has been used in oil and gas forecasting.

DEFINING BYPASSED RESERVES AND IDENTIFYING REFRACTURING CANDIDATES

A profitable refracturing intervention begins with proper candidate selection. Combined with production logging, the Weatherford Raptor 2.0 cased-hole reservoir evaluation system helps identify and rank refracturing candidate wells by determining the existing flow profile and identifying unproduced intervals behind the casing. With 250% more sensitivity than standard two-detector pulsed neutron tools, the Raptor 2.0 system delivers definitive oil and gas saturation data. Rather than a generalized interpretation of the reservoir, the system finds and defines bypassed oil and gas volumes to within a few saturation units. These logs not only guide operators in selecting refracturing candidate wells, but they also give a precise roadmap to quickly increase production with standard cost-efficient perforating. Raptor 2.0 technology is well suited to the low-porosity environments in unconventional reservoirs. The system features a large four-detector array that enhances spectroscopic carbon-oxygen and sigma measurements and is highly sensitive to all hydrocarbons, especially gas. Fully compatible with production logging and many other formation evaluation technologies, the Raptor 2.0 system reduces workover costs and downtime with a single-run candidate-selection option for reperforation, restimulation and other production- management operations.