Real-Time Dip Applications for Geosteering Horizontal Wells, Onshore Nigeria

Abstract

Geosteering is the interactive placement of a wellbore using real-time geological criteria; its use allows increasingly more complex geologic targets for horizontal producers and injectors. This paper presents a case study of Geosteering horizontal wells in an onshore field of the western Niger Delta. The results demonstrate how an integrated team uses modern LWD tools to make real-time well path corrections in a challenging environment. The objective of geosteering is to direct the well using real-time logging and interpretation to a specific target within the reservoir. Various best practices are discussed in which geologic and structural data are combined with LWD measurements to lower the risk of " landing" and subsequently maintain the horizontal portion of the well in the desired location. Real-time dip estimation is a tool in the geosteering arsenal that can assist with geosteering decisions both during landing and while maintaining the lateral portion of the wellbore in the target window. Field examples illustrate the use of azimuthal density measurements to enhance real-time evaluation and decision-making processes. Quadrant density measurements and density images are used to calculate dips and enhance steering decisions made by an asset team of geologists, petrophysicists, and geosteering engineers for a field development project in Nigeria. Present methods in geosteering for real- time dip estimation include interpretation of resistivity and density images, estimation from the quadrant density log, and detailed stratigraphic correlation during approach hole drilling. Associated with each estimation method is an inherent uncertainty with the dip calculation; these uncertainties can lead to geosteering decisions of low confidence. To reduce the total uncertainty, more than one method for calculating dip can be used to assist with well plan adjustments. The thinner the sand is, the tighter the steering tolerance becomes, requiring the well to be drilled closer to bed or target boundaries. The most accurate possible dip estimation is needed for these cases. Introduction The " Swamp" Field is located onshore in the western Niger Delta, and is operated by Chevron Nigeria Limited (CNL) in a joint venture with Nigerian National Petroleum Company (NNPC). There are presently 35 horizontal development wells and 6 horizontal water injectors in this development. Production in March 2003 was 39,800 BOPD, with 47,200 BWPD being injected. The reservoirs comprised 10 to 60 ft thick shoreface sands with occasional tidal channel facies. Lateral variability in reservoir thickness and quality demand that all horizontal wells in the " Swamp" Field be geosteered.

Geo-Steering with Advanced LWD Technologies - Placement of Maximum Reservoir Contact Wells in a Thinly Layered Carbonate Reservoir

“…[16][17][18][19][20] When the borehole intersects a bed at a high incident angle from above, the bottom log is the first to see the formation, followed by the right and left, and finally by the top measurement. The logs will appear as if the top and bottom measurements are depth offset.…”