The goal of Subsurface Containment Assurance is to ensure that no environmental damage, damage to operated assets, or impacts on well operations (drilling or production) are incurred by leakage of production or injection fluids from their intended zones. Subsurface Containment Assurance involves the integrated efforts of the subsurface (reservoir and overburden characterization), the wells (planning, construction, well integrity and abandonment) and the operations (process and well operations and management of change) teams. Disciplines must act together to develop and implement a surveillance plan to proactively monitor containment during well and injection operations. The paper will describe the elements of a Subsurface Containment Assurance Program that are required for business units operating across the entire life cycle from exploration to mature developments. The program is designed to be comprehensive yet flexible, and focuses on the critical elements and risks for individual operating units. A consistent framework has been created and implemented that draws from existing tools for reservoir and overburden characterization and field management, and combines these tools to reduce the risk of unintended subsurface fluid containment loss. Specific assessment criteria and ranking approaches and tools for qualitative and quantitative estimation of containment risks will be reviewed. Lastly, practices for deepwater subsurface containment and implications for the oil and gas industry will be discussed.
The Barnett Shale is one of the first unconventional shale plays developed with multistaged, fracturestimulated horizontal wells in the world. It is located in North Central Texas near Fort Worth. At the end of 2013, the Barnett Shale had over 14,000 multistaged hydraulically fractured horizontal wells (MFHW) with approximately 7,600 of these wells with over five years of production history. In addition to these MFHW, there are approximately 4,000 vertical wells.Production forecasting for unconventional reservoirs with MFHW is a topic with a great amount of interest. The question is what are the appropriate decline parameters to be used in the forecast? Are multisegment forecasts with their own decline parameters necessary?Currently, production forecasting using a modified hyperbolic Arps equation is still widely accepted. This work provides analysis in characterizing decline parameters during and after linear flow for horizontal wells in the Barnett Shale using public data. There will be examples of MFHWs from the Barnett where the hyperbolic b-exponent will be calculated for each month of production and shown to vary with time as flow regimes change.Single well simulation will be used to characterize the different flow regimes and their effect on decline parameters. Simulation of wells with and without volume outside of fracture tips and their effect on decline parameters will be shown. The decline parameters were in an Arps forecast to match our single well simulation forecast. Uncertainty analysis of production forecast using simulation models is also presented in this work.
The Peng Lai (PL) 19-3 Oil Field, located in the ConocoPhillips operated Bozhong 11/05 Block in the central southern Bohai Sea, offshore China, is currently the largest offshore oil field in China. The trap is a complex wrench anticline developed along the Tanchen-Lujiang fault system. The main oil accumulation is in the Neogene Lower Minghuazhen and Guantao Formations with a vertical relief from the top reservoir to the deepest oil bearing rock of approximately 500 meters. The PL 19-3 Oil Field, deposited in a fluvial environment, is a complex stacking of unconsolidated sandstone reservoirs, with moderate porosity and permeability and low net gross ratio. The trap has been divided recently into numerous fault blocks which have unique contacts and variable oil properties both vertically and laterally, with oil gravities ranging from 12 to 22 API. This paper reviews the pressure acquisition history and analysis from the 160 well formation test database, which includes both wireline formation test (WFT) and formation test while drilling (FTWD). Formation testing in the Neogene formation of Bohai Bay is challenging since the reservoir is unconsolidated and the oil is heavy. Common problems that affect pressure testing are described, efforts to enhance test efficiency are stated and key learnings and best practices to secure high quality pressure data are summarized. Conventional pressure interpretation to derive fluid gradient and oil water contacts, identify reservoir compartmentalization and flow barrier is challenged due to small density contrast between the heavy oil and water in the field. The excess pressure method, which is attributed to formation water properties and consistent hydrostatic pressure gradient in the field, has been an effective way to analyze pressure data. In this paper, the historical application of excess pressure in the industry is reviewed, examples of the excess pressure interpretation in PL 19-3 Oil Field are given and integrated interpretation practices are emphasized. Pressure data have wide application in the PL 19-3 oil field. This paper summarizes and demonstrates how original excess pressure and dynamic logging while drilling (LWD) pressure data have been used successfully to predict oil water contacts, to analyze fault transmissibility, to monitor water flooding efficiency, to identify fluid properties, to interpret fault cuts in wells, to optimize mud weights while drilling and to mitigate risk and well bore damage during completion operations
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