Unique Bi-Center Technology Delivers in Demanding Directional Applications

Abstract

Hole-opening on directional motor assemblies has always been problematic. This is due to the fact that mainstream string hole opening tools cannot be used due to lack of rotation during periods of sliding. As such, use of bi-center hole opening bits have increased in an attempt to drill and open the hole in one run with a directional motor. This paper documents the development of a unique bi-center design to provide not only reliable hole opening, but also high and consistent dogleg response on a motor assembly. The project is focused on a drilling program within the Uracoa field in Eastern Venezuela (Figure 1). This application called for a build from vertical to horizontal, with maximum dogleg severity (DLS) requirement of 10.2deg/100ft. This had not been attempted in the past with bi-center bits, relying instead on conventional 8 ½" PDC bits. However, the operator had hole problems that made running 7" casing difficult in this section. To get the casing to bottom, a number of wiper trips were required to condition the hole. In order to reduce the non-productive time, a bi-center and directional motor were selected by Petrodelta / PDVSA to eliminate the additional wiper trips required with the conventional fixed cutter (FC) bits: The 8 3/8 x 9 ½" bi-center would effectively drill a larger hole size. The unique design selected features a mid-reamer section. This double profile design is considerably more stable than prior technology, delivering improved borehole quality and enhanced directional performance. The initial application was extremely successful. The elimination of the wiper trips and hole problems considerably reduced drilling time for the section, and the casing took notably less time to run. This amounted to $960K savings compared to the field average and $1.69 million compared to the previous well drilled. In addition, the required DLS was achieved while increasing ROP by 58% compared to the field average. The latest bi-center technology, in conjunction with Steerable motors, can deliver the required DLS and enlarged hole in demanding directional applications. This has proven to be an extremely cost-effective drilling system, saving nearly 10 days compared to the field offset. Introduction The Uracoa field is situated within the Temblador group, a miocene sedimentary unit located in Monagas state in Eastern Venezuela. Within the main area are the oilfields of Temblador, Isleño, Pilón, Uracoa, Bombal, Tucupita, El Salto and Jobo-Morichal (Figure 2). All fields in this area are similar in their stratigraphy and predominantly consist of the Mesa, Las Piedras, Freites, and Oficina formations (Figure 3). The specific application requires drilling the intermediate hole section (8 ½") through the Freites and Oficina formations. The Freites (late medium Miocene) consists of very hydratable claystones, unconsolidated shales and fine grain sandstones. In contrast, the Oficina formation (medium early Miocene) consists mainly of compacted shales, interbedded with a mixture of very fine grain and fine to coarse grain Oficina sandstones and thin beds of lignites. The sandstones occur in thicknesses ranging between 30 and 200', and constitute the main pay zone. API oil gravities range from 12 to 19 degrees.