The present paper describes performance improvements and well safety achieved with the use of Managed Pressure Drilling (MPD) in the exploratory block of Parva Negra Este, in Neuquén Basin. Petrobras Argentina S.A (PESA), with the technical support from the Petrobras’ headquarters, in Brazil, drilled two exploratory wells applying MPD and targeting Vaca Muerta shale oil & gas play. High-pressure zones characterized the drilling scenario, reaching, usually, pore pressures higher than 18 lbm/gal in unconventional reservoirs, composed of tight sand and shale. The use of MPD in both well constructions was quite efficient, including well control and plug and abandonment (P&A) operational applications. Those operations proved that MPD can effectively replace the Under-Balanced Drilling (UBD) system, which is standard practice in that area. In the first well, PESA reported significant gains in drilling performance when compared to other wells previously drilled. Drilling with MPD did not record non-productive time (NPT), differing substantially from the previous wells constructed in the surroundings of Parva Negra Este with an average NPT of 20 days. A considerably larger recovery of coring samples was achieved, being also possible to eliminate one well section, by drilling two zones of interest in a singlesection. Additionally, lessons learned were implemented, resulting on higher rate of penetration (ROP) with the support of MPD. In the second well, a high overpressurized pore zone was reached, leading to a very complex well control event followed by a permanent P&A operation. The formation pore pressure was much higher than the expected for the area. Instead of using an 18 lbm/gal drilling fluid, it was necessary to weight the fluid up to 21.3 lbm/gal, adding hematite as weighting material. In that scenario, the use of MPD made the operations of circulation and well cementing safer than with the conventional drilling approach utilized in that vicinity. The application of Dynamic Formation Integrity Tests (DFIT) and Dynamic Pore Pressure Tests (DPPT) ensured a more precise operational window, helping to formulate risk matrices for safely pulling the drilling string out of the hole. In addition, the precise definition of the operational window was a valuable information to plan the best approach for P&A. Besides performing those tests, the MPD system was very useful to evaluate operational parameters and verify how effective was the settlement of the abandonment cement plugs. In summary, MPD supported safer drilling and P&A jobs, better drilling performance and greater information achievement through more efficient well logging and sample coring.
This paper provides an overview of the main efforts that are being endeavored by Petrobras in order to contribute for developing a Brazilian regulation for use and discharge of drilling fluids and cuttings from offshore oil and gas operation, based on operational safety, well integrity and environmental aspects. In early 2018, the Brazilian Environmental Agency launched a Normative Instruction (IN 01/2018) addressing some new conditions for use and discharge of fluids and cuttings from offshore drilling rigs. This regulation is based on the EPA rules, although some relevant points deviate from it, such as the prohibition for discharging drilling fluids and cuttings associated with hydrocarbon reservoir sections. Additionally, this regulation mentions a potential zero discharge by 2022. Due to the challenges for meeting these new requirements and some uncertainty about the real environmental benefits, Petrobras has been developing fundamental and applied studies, research development and protocols in this area. Petrobras settled an innovative governance model to deal with the new regulation, its consequences and interfaces. It works as a multidisciplinary committee coordinated by an executive manager. It involves a law support for environmental issues and four work fronts, such as (1) linking between internal and external organization (2) guarantee of providing the required infrastructure (3) economical and operational impacts (4) technologies (research, development, studies and protocols) dedicated for related matters. Concerning the forth front, seven important initiatives were initially addressed and cover topics such as operational safety, well integrity – including offshore wells dedicated to cuttings disposal, laboratory protocols and environmental issues. Some relevant studies are those concerning LCA (life cycle analysis), options for avoiding landfill as final cutting disposal onshore and the quantification of oil compounds in drilling fluids and cuttings from the pay zone well section. The lack of knowledge about the whole impact for onshore destination as drilling waste management strategy, the improvements that still have to be established in order to achieve better operational practices and the comprehension of the input of oil from drilling discharges are the main drivers of this paper. The results help to clarify cloudy topics and, consequently, contribute to create a new basis for building or revisiting some aspects of the present regulation.
The use of micronized weighting agents, in multiple operations, have become more commonplace over the years, with current applications now going far beyond their targeted original purpose of reducing pressure losses in extended reach wells. This specific case reports the development of a fit for purpose system engineered to tackle multiple challenges such as: limitation in using heavy density brines composed of bromides in an offshore environment; hydrate suppression under Drill Stem Test (DST) conditions; weighting agent sagging control; plugging of downhole tools due to heavy solids loading; proper pressure transmission for downhole tools activation; and formation damage prevention. The operation involved the following steps: 1 - development of a Water-based Micronized Weighting Agent Fluid System (WBMWAFS), laboratory testing, simulation evaluation and testing validation for all target properties; 2 - development of an appropriate DST approach with the usage of a designed set of explosives to minimize formation damage and the interaction of the DST fluid with such cargos; and 3 - the evaluation of the overall system performance in order to validate the integrated approach used to design such solution. The DST results indicated that the WBMWAFS is capable of delivering all the technical requirements for a trouble-free operation, with no significant register of weighting agent sag, hydrates or with any variation in fluid properties, whilst enabling a DST operation that demonstrated a negative skin damage during the clean-up period and no damage associated with the WBMWAFS. The WBMWAFS performance opens the possibility of the application of this type of fluid as a replacement for high-density clear brines in many challenging environments.
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