Methodology of Effective Lateral Placement for Underbalanced Coiled Tubing Drilling Wells

This paper describes a methodology that has been developed to maximize lateral placement in productive reservoir intervals during underbalanced coiled tubing drilling (UBCTD) operations. UBCTD has emerged as an effective and economically viable development solution for exploiting reserves in mature gas reservoirs. In some cases, it can be a suitable solution to develop reserves in more geologically complex and heterogonous reservoirs over the conventional drilling and stimulation techniques. The methodology integrates big surface and subsurface data from multiple sources in multiple formats in real to near real-time that are normally acquired during UBCTD drilling operations. The multiple sources of data include subsurface geology, wellsite biosteering, reservoir influx, well testing and drilling, and can provide important information about the reservoirs encountered. With the aid of data analytics and an advanced visualization tool, the data is translated into in series of engineering plots that enable easier identification of productive intervals and more informed as well as efficient lateral placement decisions. This methodology has proven superior to the conventional instantaneous Productivity Index (PI) approach that is commonly used for UBCTD lateral placement. The methodology has been tested with good success in a number of recently drilled UBCTD wells in geologically complex depositional environments across carbonates and clastic reservoirs. Post flowback and pressure transient test analyses have shown significant improvement in the well deliver abilities and effective lateral lengths. Past performance from wells drilled using the PI method will be compared with wells drilled with this method.

A Successful Field Application of Polymer Gel for Water Shutoff in a Fractured Tight Sandstone Reservoir

The wide existence of fractures makes conformance control by polymer gels more challenging in water-flooded oil reservoirs. Selection of an applicable gel system and design of an intelligent approach for gel treatment are key components for a successful field application. Moreover, selecting the candidate wells and determining the injection volume of gel are also critical to the success of gel treatments. A gel system with adjustable polymer concentrations was applied for conformance control in fractured tight sandstone reservoir, and notably, less than 5% of syneresis was detected after aging for one year at reservoir condition. The viscosity and the gelation time of this gel system can be adjusted according to the targeted reservoir conditions. The pilot test was conducted in Huabei oilfield (China), and the oil recovery after water flooding was only about 20% original oil in place (OOIP). With further exploitation of the oil field, the majority of the reservoir has suffered from poor sweep efficiency and extremely high water cuts. To characterize the distribution of fractures, the seismic coherence cube was utilized. In addition, the pressure transient test, interwell tracer test and the injection-production data were used collaboratively to determine the volume of fractures in the reservoir. The option of gel formulation and the determination of operational parameters are mainly based on the wellhead pressure. According to the seismic coherence cube, the zone of candidate well group shows a weak coherence state, indicating that numerous fractures exist. Furthermore, there is good continuity between the candidate injection well and the production well. According to the pressure transient test, the volume of re-open fracture is about 1730.9 m3, while the volume of micro-fracture is about 4839.4 m3. Comparably, based on the interwell tracer test, the estimated volume of fractures is approximately 3219.7 m3. Consequently, the designed volume of gel for treatment is 1500.0 m3 in total. The properties of gel slugs were carefully designed, which was tailored to the specific wellbore conditions and formation characteristics. Three months after the gel treatment, the average oil production was increased from 0.36 t/d to 0.9 t/d, and the water cut was decreased from 95.77% to 88.7%. The improved oil production was still benefited from this gel treatment after one year. This study provides a comprehensive approach, from optimization of gel formulation, followed by selection of candidate wells, to calculation of the injected volume, to design the viable operational parameters, for gel treatment field application in fractured reservoirs. It shows that, besides a gel system with superior properties, a suitable injected volume of gel may enhance the chance of success for gel treatments.

Diagnostic Plots of Pressure Transient, Rate-Transient, and Diagnostic Fracture-Injection/Falloff Tests

All transient test interpretation methods rely on or utilize diagnostic plots for the identification of wellbore or fracture storage distortion, flow regimes, and other parameters (e.g., minimum horizontal stress). Although all "test" interpretations of interest are transient test data (i.e., those involving an "event"), the associated diagnostic plots are not interchangeable between such tests. The objective of this work is to clearly define the appropriate diagnostic plot(s) for each type of transient test. The work applies the appropriate transient test theory to demonstrate the applicability of each diagnostic plot along with clearly defining the characteristic features that make a given plot "diagnostic." For pressure transient testing, the material is largely a review, but for rate transient tests and diagnostic fracture-injection/falloff tests, new ideas are introduced and documented to justify appropriate diagnostic plots. Data examples are provided for illustration and application. In general, pressure transient test diagnostic plots are not misused, but the same cannot be said for diagnostic fracture-injection/falloff tests (or DFITs) where it is common to ascribe flow regimes and/or draw other erroneous conclusions based on observations from an inappropriately constructed or interpretated diagnostic plot. The examples provided illustrate both the correct diagnostic plot and interpretations, but also illustrate how data can be easily misinterpreted in common practice.