Definitive Survey Methodology – Update to an Old Concept for Higher Reliability

Abstract

Abstract Data quality assurance applied to well positioning optimizes contingency plans to reduce the time to drill a relief well and provides greater reliability in autonomous and remote drilling operations. In addition, it provides the highest degree of agreement with the well design, making it possible to reach the best productive zones of the reservoir and avoid geological risks. This data quality assurance procedure supports the construction of high-productivity wells in the offshore pre-salt fields in Brazil. The objective of this work is to present the results of the Definitive Survey Methodology in pre-salt wells, to improve the survey quality assurance and the reduction of uncertainty ellipses - during operation and in real-time - using two survey tools with different physical principles. The Definitive Survey Methodology promotes the verification of error models of the survey tools and reduces the Ellipses of Uncertainty (EOU), well to well, creating an external directional data quality assurance, which goes beyond specific internal quality controls used by service companies. The methodology consists of the use of three tests that compare independent surveys. The first and second tests are statistical, Relative Instrument Performance (RIP), and Chi-square, in which the reliability of the used error models is verified. The RIP test is a comparison that produces results with quantitative values about the agreement of overlapping surveys. The Chi-square test is a quality fit test that compares two surveys and their compliances with their error models. The third test is a qualitative geometric test that compares the uncertainty ellipses of different survey tools at the same depth, allowing a quick interpretation of graphic representations and can be applied during or after drilling. The methodology was applied in four pre-salt wells named in this paper as Well_A, Well_B, Well_C, and Well_D. The final measured depths of the wells range from 5078m to 6801m. The tools used were: gyro while drilling (GWD) for all inclinations in real-time (inrun), GWD outrun memory mode (OMM), drop gyros, and measurement while drilling (MWD). The methodology resulted in a reduction of 74.55% (Well_A), 50.93% (Well_B), 33.69% (Well_C), and 60.05% (Well_D) of the ellipse of uncertainty at the top of the reservoir. The use of the Definitive Survey Methodology enhances the quality of the directional data, verifying the error models used well to well. The reduction of uncertainties provided by the gyroscopic tool ensures the reliability of the contingency plan and the entry into the top of the reservoir. Consequently, by optimizing the positioning of the wells, it is expected to make the most of the natural resources in the long term, while also building safer contingency plans, and making the extraction activity of this natural resource more sustainable.