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Results
Depositional Controls over the Lacustrine Source Rocks of the Cuyana Basin. An Approach to Model a Mechanical Cyclicity Through an Integrated Analysis of Sequence Stratigraphy, Petrophysics and Rock Properties
Barredo, S. P. (Instituto Tecnológico de Buenos Aires) | Sosa Massaro, A.. (Instituto Tecnológico de Buenos Aires) | Fuenmayor, E.. (Instituto Tecnológico de Buenos Aires) | Abalos, R.. (Instituto Tecnológico de Buenos Aires) | Stinco, L. P. (Oleumpetra) | Abarzúa, F.. (Universidad Nacional de San Juan)
Abstract Integrating field and laboratory data is possible if there are strong geologic criteria to relate them. This challenge demands understanding rocks from the fabric and mineralogy up to the architectural elements of rock bodies at a basinal scale. The geological properties of rocks, being them clastic, chemical or biochemical, influence reservoir quality and hydrocarbon producibility, but continental mudrocks/siltstones (shales) are by far more complex because of their depositional nature and highly variable vertical and lateral sedimentary characteristics. Grain size variability and sedimentary structures are common in these rocks. From outcrops, well logs and the source rocks of the Cuyana Basin (Argentina) could be characterized as deposited in lacustrine environments under a strong tectonic and climatic influence. Silty sandstones, limestones, massive and laminated bituminous shales developed in underfilled and balanced to overfilled lakes. They display parallel/inclined/rippled laminations, coarsening/fining upwards patterns, nodules, scour surfaces and pedogenic features. Total organic content may reach 14 % and corresponds to macro and micro floral remains, freshwater invertebrates and kerogen types I and II. These lithofacies are vertically stacked in patterns that can be related to cycles with different mechanical properties. In outcrops and with the help of seismic lines third order depositional sequences representing basin variations in accommodation space were recognized as low accommodation (LAS) to high accommodation (HAS) sequences developed in each of the three rifting stages. Using detailed information about mineralogy and fossil content climate was characterized and fourth order parasequences could be characterized. Fifth order (bedset-rhythms) cycles were interpreted on the basis of outcrops and well logs. Inorganic (especially clays) and organic content, pedogenic fabric, burrows and microfracturing represent weakness planes and as they vary according to these cycles, it was possible to model a mechanical cyclicity along the whole lacustrine column and to analyze their depositional controls. This integrated study has provided relevant data for the understanding of the geological and mechanical properties that will contribute to the optimization of fracture programs.
- Geology > Sedimentary Geology > Depositional Environment > Continental Environment > Lacustrine Environment (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.57)
- Geophysics > Seismic Surveying (0.86)
- Geophysics > Borehole Geophysics (0.86)
- South America > Argentina > Patagonia > Neuquén > Neuquen Basin > Vaca Muerta Shale Formation (0.99)
- South America > Argentina > Cuyo Basin (0.99)
- South America > Argentina > Cuyana Basin (0.99)
- (4 more...)
Abstract The development of the Levas field began in 1952, by drilling vertical wells using a water-based drilling fluid, however, from 1998 when the aggressive drilling of deviated wells began, also the operational problems started in the middle section, problems such as tight hole, drag, hole instability, stuck pipe, and others. In 2002, the company decided to switch to oil-based mud to reduce and control the incidence of those inconveniences. PDVSA Services San Tome, began searching for a special drilling fluid to replace the existing, due to high demand of the main component of the oil-base drilling fluid (Vassa), and its low supply due, and more important the high cost and environmental difficulties to treat and dispose this kind of drilling fluid and the cuttings. This study evaluated four sets of high performance water-based drilling fluids, to start a new development stage for drilling deviated wells at the Levas Field. To determinate the technical feasibility, some studies were made, first the physical properties, such as: rheology, filtration, solids percentage in the system, and others, were evaluated to make a comparative analysis to find out which water-base drilling fluid had the best performance considering the geological and operational conditions of the field. Also the mineralogy (clay minerals) of the field was determinate through the X-ray diffraction test, which concluded that the predominant mineral of the field was kaolinite. This clay has a low CEC value that means it has a high dispersion capacity. This result allowed to determinate one of causes of the hole instability in the middle section of the deviate wells. Additionally, the Dynamic Linear Swell test was made to determinate the inhibitory capacity of each water-base drilling systems with the clays from the formation and bentonite, beside the clay dispersion test evaluated evaluate the capacity of each high performance drilling fluid systems to maintain the integrity of the body shale and cuttings. Finally, the cost analysis allowed evaluating the economic feasibility of each drilling fluid system. After analyzed the various results, we concluded that the drilling fluid trading system number one had the best cost benefit to drill deviated wells in Levas Field.
- Geology > Mineral > Silicate > Phyllosilicate (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.40)