The Saudi Arabian Oil Company (Saudi Aramco) operates one of the principal high profile extended reach drilling (ERD) projects in the world. This is accomplished through the development of a sizable number of horizontal wells categorized according to the total depth. Wells with the shortest vertical displacement have been significantly optimized during the project execution thereby reducing the room for enhancement. The drilling engineering team conducted a comprehensive evaluation of the existing casing scheme and problematics along the M field. A new approach was devised to redesign wells with a total depth up to 17,600 ft. The aim was to achieve a substantial improvement in drilling performance and potential savings for the remainder of the project. ML-1 and MO-1 were selected as candidates to implement the novel alternative; both drilled from different platforms where several wells have been previously completed using the standard design. Drilling troubles, such as loss of circulation and hole instability, occurred during the execution of such wells leading to major lost time. The solution comprised the optimization of the well trajectory, slim-down the upper hole sections and combine the lower ones, drill longer intervals and set casings deeper to cover problematic zones without compromising the well integrity. The detailed engineering study included a probabilistic analysis to evaluate the economic viability of the landmark application. Two wells were successfully drilled and completed applying the downsizing strategy. The impact of anticipated challenging events in both 12 1/4-in and 8 1/2-in holes was decreased as a result of the new design. The implemented preventive plans led to a rapid elimination of encountered challenges. This optimization produced a combined 27% reduction in drilling time, and minimal non-productive time (NPT) with associated global cost savings of 39% compared to a large hole string design. Finally, this new approach in a still ongoing project along with the feasibility of extending it to other areas will lead to potential improvement in well delivery and operating cost.

Complexity and heterogeneity inherent to naturally fractured reservoirs pose important technical, economic, and managerial challenges to operating companies. In order to meet these challenges, operators ought to apply innovative technologies and tailored exploitation strategies. This paper summarizes the reservoir surveillance and characterization approach, as well as the operational strategies used in the development of the Cretaceous fractured carbonate Cogollo Group in La Concepción Field, western Venezuela, with emphasis on the successful application of selective technologies and methodologies. Discovered in 1948, the Cretaceous reservoir had produced over 90 MMSTB of 36°-API oil from 29 wells up to January 2005. Since 1998, Petrobras EnergÍa Venezuela's operations have resulted in a significant increase of the total reservoir oil throughput from 2500 to a maximum of circa 17000 BOPD, with an associated cumulative production of 23 MMSTBO. A key factor in the successful redevelopment of the mature Cretaceous reservoir was the timely recognition of the major features driving the reservoir productivity and performance, in addition to the opportune identification of the main operational risks and the suitable technology to mitigate them. Then, as we drilled and intensively acquired data, we refined the reservoir description, improved operational indicators and costs, and implemented new technology and risk management strategies to face the increasing challenge of the remaining reservoir targets. The integration of the new structural model (en echelon transpressional stepover zones), derived from the 3D seismic data, modern well-logs and dynamic (production logs and pressure tests) data acquired from re-entries and new wells, and rock description and analysis from 950' of core, allowed us to define a clear relationship between fault-related fracture systems and production. In brief, the Cretaceous reservoir is classified as a type-II fault-related fractured reservoir containing a micro-fissured pseudomatrix. Currently, based on our model, the main development strategy is to drill wells that cross "seismically visible" faults with the aim of intersecting their associated fracture networks. Discontinuity seismic attributes are used to delineate the fault zones and optimize well locations. Reprocessed seismic volumes are now used to diminish the uncertainty in the spatial geometry of the targeted faults. In addition, the structural interpretation is being tested and enhanced with the results from physical experiments (sandbox analog modeling). Presence of discrete highly productive fractured zones, in conjunction with low reservoir pressures due to depletion, led to the adoption of under-balanced drilling (UBD) with Nitrogen injection as the drilling technique in the reservoir section to avoid severe circulation losses. During the UBD phase, a calibrated drilling dataset is used along with mudlogging data to check for geological events and monitor well productivity in real time. Furthermore, the complexity and uncertainty associated to the targets impose the use of strict directional control to conform to the designed complex well trajectories. The presented field development strategy has proved to be successful since it has enabled to achieve a sustained economic oil production in the naturally fractured Cretaceous reservoir of the mature La Concepción field.

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This study is intended to show that it is possible to reduce risks, time and costs in well drilling through application of Geomechanics in marginal fields. It refers to the Oritupano-Leona field, East Venezuela, which has more than 700 wells drilled from 1938, 29 of which are horizontal wells. In spite of the production success, 6 over 29 wells, 25%, presented problems due to hole instability that lead to several stuck pipes, sidetracks and down time. Drilling parameters of 23 horizontal wells, operational problems, geomechanical information and regional geology were considered for this analysis. Problems associated to mechanical/chemical instability and operational problems were identified. Geomechanical parameters were calculated and analyzed with the specialized software considering pore pressures, mud density, minifrac and electrical logs, where the stress direction was studied with the interpretation of imaging logs and review of the regional stresses. A friction diagram adjusted to the wide of the breakout was applied, whereas vertical stresses were calculated through density log integration. Rock mechanical parameters were product of RSD tests that included rock mechanical resistance analysis (UCS), determination of the internal friction angle and the Poisson's ratio and Young modulus, calculated with the use of neural networks. Drilling events were visualized in order to define the stability frame of the area for the different operational parameters based in geomechanical parameters previously calculated. With this data a new well design was elaborated integrating trajectory optimization and operational parameters in order to diminish the stability problems. Different mechanical instability values were identified in the study in three zones of the field, and the safe operating window for drilling and operational parameters was identified for each one, guarantying hole cleaning. The application of the criteria and recommendations of the results of this study had an outstanding impact on the horizontal well drilling in the Oritupano-Leona field. In 2005, a new record was established with the drilling of the ORM-174, which is the fastest horizontal well drilled in the field history. Two other wells were drilled in 2006 with excellent results. Introduction The Oritupano-Leona unit is located in the Venezuelan Oriental Basin (Maturin sub-basin) along Anzoátegui and Monagas states. Its extension is 1600 km2 with 23 oil fields in eight (8) sets or geographical units. It was discovered in 1938 and it has been operated by different companies: TEXAS, MGO, BARCO, PDVSA, and since March 1994 to date Petrobras EnergÍa Venezuela, S.A (PEVSA). The productive intervals are represented by the Oficina Formation that belongs to the Early/Mid Miocene -composed by sandstones of outstanding petrophysical characteristics and siltstone, shale, lutites and lignite associated to a transitional fluvio-deltaic environment with tides. The multiple productive levels of the various fields are within a depth range between 4,500 and 11.000 feet. Since the discovery around 700 wells have been drilled (over 200 by PEVSA), including around 25 horizontal wells. Figure 2 shows the design of a typical horizontal well. This study emphasized regional geology, the characteristics of the field, geomechanical, well construction, optimal trajectory, well design, optimization of drilling parameters and risk analysis.