The exploration campaign that started with the creation of the new company, in 2007, took another step forward with the drilling and completion of it's first horizontal producing well in the Campos Basin. The Waimea accumulation was discovered in the third exploratory well drilled in December 2009 (1-OGX-3-RJS), and confirmed with formation tests. The main reservoir drilled in well 1-OGX-3-RJS contained high energy carbonates intercalated with shales, occurring in structural and stratigraphic traps limited by normal and compressive geological failures in the NE-SW direction. To ensure the commercial production of this accumulation, the development plan will require the drilling of several horizontal wells with high productivity index. This paper explains how careful planning along with well placement technologies were used to mitigate the geological uncertainties involved in drilling a horizontal well in a carbonate reservoir. The result was a successful production well at an early stage in the exploratory campaign. Some of the key design and operation aspects which contributed to the success of the well were:–The initial design objective for the Waimea Extension well was to define a directional well profile and a linked horizontal profile such that both intersected at the planned entry point of the horizontal section, this challenging approach was key to obtaining further knowledge of these highly fractured carbonate reservoirs.–The evaluation of several alternative trajectories with the seismic data and, proper petrophysical properties analysis from the pilot hole log data to maximize well bore contact with the reservoir, to achieve the highest possible net pay in 1000 meters of horizontal geosteering.–The development of a geomechanical study to review these trajectories and define mud weight windows for safe drilling with minimum fluid invasion.–The use of well placement technologies with the support of, fit for purpose, rotary steerable system with logging while drilling tools which provided vital real time formation evaluation data for geosteering. The planning and execution of the well culminated in excelent results for this first horizontal producer, with high net pay over the 1000 meters drilled and well testing confirming the well's high production potencial.

This paper describe in details the design and successful operation of an acid diversion completion system, which was used for first time in an exploratory project offshore Brazil. The most significant discoveries in a recent exploratory campaign in Campos Basin were in carbonate reservoirs. The first vertical well test showed a high heterogeneous and natural fractured carbonate reservoir. Considering the reservoir characteristics, analytical and numerical modeling was performed to assess the productivity of horizontal wells compared to vertical wells. As part of the Operator strategy of developing this oil field using maximum reservoir contact, a well test evaluation project in the open hole section, mitigating the risk of reducing the production, fractures cementation, etc. was performed. The whole project was developed to address the challenges of carbonate horizontal wells i.e. low permeability sections contributing marginally to the total production. A multistage horizontal open hole completion was designed and installed to perform a separately and selective stimulation in more than 3,000 ft of horizontal section. Previously, the most advanced technologies for open hole completions with mechanical isolation were reviewed to have the ability to perform multiples stimulations (fracture or matrix) in one continuous and more efficient operation. Based on final reservoir data obtained during the horizontal open hole navigation and a calibrated Geomechanical model, the acid diversion completion system was selected to perform an acid stimulation instead of a high pressure acid fracture job. The application was successfully run in this anisotropic carbonate reservoir and eight compartments were stimulated using an acid plant and high pressure pumps mounted on a Supply Boat dynamically positioned. More than 1000 barrels of stimulation fluid; a mixture of hydrochloride acid, and a visco-elastic agent to improve diversion were pumped stage by stage to the reservoir with a real time monitoring at the operator Support Center in Rio de Janeiro. After all the stimulation jobs and to prevent the high fluid losses, the well was shut in downhole using the reservoir formation isolation valve. A DST string was run. CT and Nitrogen were used to kick off the well and after 6 hours the well started to flow naturally, with first oil at surface within the first 8 hours of flow.

The use of an eight-inch diameter formation-tester-while-drilling tool for 12 ¼ into 16-in. holes has provided the option to significantly if not totally replace wireline logging operations in pilot sections of planned horizontal wells in Brazil. When using LWD tools only, sections of a pilot interval do not need to be plugged and abandoned, as had been the practice. The option with a complete suite of LWD tools can greatly reduce operational risks and save time and money. Savings of up to six rig days and US$ 900.000,00 can be expected. In the past, a 12 ¼ in pilot section was drilled before the horizontal section of a planned horizontal well was developed. The purposes of the pilot section were to confirm top and base of target reservoir and evaluate its production characteristics. While drilling pilot sections, the LWD tools were limited to gamma, resistivity and pressure while drilling. Thereafter, a more comprehensive wireline logging suite was run including, wireline-run formation testers. To avoid the need for a costly pipe-conveyed logging runs, these sections were also limited to inclinations less that 50 degrees. After the logging runs, the pilot sections were typically plugged and abandoned with a sidetrack section drilled off the top of the last cement plug. The availability today of LWD formation tester allows for a new and less costly option. The 12 ¼ in. section of the planned well takes an S-shape profile, getting close to the target reservoir at inclination higher than called for in running wireline, dropping off to reach the base of the reservoir and continuing to its final TD destination. It is not necessary to plug and abandon all the pilot section, and the planned drilling, including logging, can be completed more quickly and efficiently. Introduction With the introduction of the 8 inches GeoTap (Sperry's formation tester while drilling tool for 12 ¼ to 16 inch holes), the wireline logging operation in the pilot wells can be restricted or even totally replaced. A long section of the pilot can be kept for the subsequent horizontal well, greatly reducing operational risks. Time and cost savings up to 6 rig-days and US$ 900.000,00 can be expected. In this paper, we will evaluate the savings in development wells where it is possible to use the LWD tool set replacing conventional wireline logging, when drilling 12 ¼ inches pilot well. To help understanding the proposal either from the point of view of the well construction engineers, the reservoir engineers and the geologists (which are normally involved in the planning and execution of the job), some basic concepts on drilling, logging and logging-while-drilling were inserted in the paper.

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