Real-time data allowed the geosteering service engineers to visualize the well trajectory at all points and make all necessary changes in the geological model, keeping the well in the zone of interest and significantly increasing production potential.

Ecuador’s state-owned oil company Petroamazonas is the operator of the heavy oil Eden-Yuturi field remotely located in the northeast Amazon region. Petroamazonas was presented with a challenge of increasing oil production in what was already their highest producing field, while minimizing non-productive time. For horizontal well EY-C91H, placing the well in the cleanest, most permeable portion of the reservoir, as high as possible on the structure, but without penetrating the overlaying cap rock shale or dropping down in the water bearing zone, was paramount. The intended target for this horizontal well was Sandstone M-1, one of the main producing reservoirs in Ecuador’s eastern basin with more than a billion barrels of oil produced to date.

A thick shale layer above the reservoir and the well-defined oil-water contact lower boundary are complicated by a kaolinitic interval, which is generally located between the shale caprock and the high permeability good quality lobe of the reservoir. Given this structure, optimal well placement focused on staying high above the oil-water contact without penetrating the kaolinitic zone. Any exit in the kaolinitic interval would be nonproductive and likely cause drilling problems.

Traditional wellbore imaging sensors and deep non-azimuthal wave resistivity could not achieve optimal placement in the interval. Wellbore imaging instruments identify the relative dip and azimuth of geological events intersecting the well bore, but the information is clear only after leaving the reservoir. Non-azimuthal wave resistivity predicts the impending intersection with a reservoir boundary, but without foretelling the azimuth of approach. In the first instance, proper decisions can be made only after exiting the reservoir; in the second, proper decisions require other knowledge as to the probable direction of the approaching boundary.

Given the challenge to reach and remain within the target interval of clean sandstone with good permeability, Sperry Drilling services demonstrated a systematic approach to well construction and delivered an integrated package of services including performance motors, the Geo-Pilot point-the-bit rotary steerable system, logging-while-drilling (LWD) triple combo complete with proprietary InSite ADRazimuthal deep-reading resistivity sensor, and StrataSteer 3-D geosteeering software.

Drilling optimization

There are three areas of drilling optimization expertise that are targeted to provide the most value to the well construction process; 1) drillstring integrity, focusing on prevention of mechanical overload, protection from fatigue, and minimizing excessive shock and vibration; 2) hydraulics management, focusing on maintaining annular pressures within wellbore pressure boundaries, optimizing hole cleaning and clean-up cycles, optimizing circulating system pressures, maximizing rate of penetration (ROP) without exceeding mud weight windows, and optimizing tripping time; and 3) wellbore integrity, focusing on defining upper and lower wellbore pressure limits, and identifying the optimum mud weight window.

The company’s drilling optimization engineers delivered analysis and solutions to optimize drilling rates, improve operational efficiency, and minimize the impact of unplanned events. They followed the “model, measure, optimize” process, which leverages Halliburton’s specialized software, using surface and downhole measurements to achieve these objectives. Improved drilling performance was delivered by using all available downhole and surface measurements to establish the exact conditions at any point in the drilling process.

When preparing for geosteering with data from the deep-reading azimuthal resistivity sensor, a series of pre-well models were run to visualize in advance the responses expected from the various spacings, curves, and images. The customized solution helped to reduce the risk through careful analysis of the geology, the well plan, and the requirements of the target well and reservoir. Based on the prewell model, an optimum set of log curves and images was selected to be pulsed to the surface for real-time decisions.

The horizontal lateral of this well was programmed for three sections—16-in., 121?4-in., and 81?2-in. using casing of 133?8-in., 95?8-in., and 65?8-in. screens. After pre-modeling and drilling the 16-in. interval, the 121?4-in. section was successfully drilled with conventional motors and LWD combo from 5,093 to 7,995 ft (1,552 to 2,437 m). Drilling the 1,106-ft (337-m) 81?2-in. section followed, using the cornerstone of the company’s Pilot Fleet of automated drilling systems, the Geo-Pilot point-the-bit rotary steerable system with at-bit inclination sensor, and an LWD suite with a deep-reading azimuthal resistivity sensor.

Real time at-bit steering control

Using point-the-bit technology, the company’s rotary steerable system precisely steered the wellbore while rotating the drillstring to increase ROP and reduce drilling time. The service delivered real-time continuous at-bit steering control and formation evaluation to provide an accurate assessment of the wellbore position at all times.

The most critical real-time data required for drilling directional wells is the angle of inclination. However, for years drillers have been forced to perform with measurement-while-drilling survey tools located 50 to 75 ft (15 to 23 m) or more behind the bit, leaving the directional driller to infer the directional behavior of the bottomhole assembly. Only after 50 ft (15 m) or more of blind drilling can a directional driller really know what may have resulted from a change in drilling parameters. This can lead to wasted drilling time and seldom results in the smoothest well path. The company’s at-bit inclination sensor helps reduce this inefficiency and uncertainty. While drilling the Petroamazonas EY C91H well, the at-bit inclination sensor, located 3 ft (1 m) above the bit, communicated real-time inclination measurements while drilling, affording fast decisions for any corrections required to modify the drilling parameters.

The target depth of 9,100 ft (2,774 m) was drilled in one run of 31.83 hours, with an average ROP of 35 ft (11 m) per hour. The well’s final true vertical depth (TVD) of 6,550 ft (1,996 m) was 19 ft (6 m) TVD below the top of the M-1 principal sand and 8 ft (2.4 m) TVD below the kaolinitic interval. Delivery of the 306 ft (93 m) interval in two days eclipsed the planned time of eight days. The well was successfully steered and remained in the “sweet spot” of the reservoir, yielding a successful well with maximum reservoir contact.

Staying in the zone

The deep-reading azimuthal resistivity sensor, capable of acquiring data in 32 discrete directions around the tool and at 14 different depths of investigation, up to 18 ft (6 m) into the formation, together with the geosteering service provided a fully compensated, multiple-depth resistivity measurement, real-time petrophysical evaluation and stratigraphic navigation solution in one package. The sensor’s deeper readings improved reaction time and allowed for increased drilling speed and the ability to steer the wellpath into the best reservoir target, achieving a longer lateral reach than predicted in the model. Geological uncertainties were reduced, drilling operations were optimized and an improvement in net pay was delivered.

Maximum reservoir contact

Real-time data allowed the geosteering service engineers to visualize the well trajectory at all points and make all necessary changes in the geological model, keeping the well in the zone of interest and significantly increasing production potential. This contributed to the resulting savings of an estimated 6.5 days in drilling time.

The well is now horizontal and remains within the best portion of the reservoir, high on the structure but clear enough from the roof and from the kaolinitic (sand) formation. In addition to saving money from reduced drilling time, Petroamazonas is experiencing increased recovery, as the current oil production of 3,300 b/d more than doubles the planned 1500 b/d.

A review of the real-time decisions after the fact showed that they were all well guided and justified, yielding a well with maximum reservoir contact from the time it reached the target sand. The multifaceted drilling optimization approach employed by Sperry demonstrated that when the technology is chosen well and applied correctly, the results are exemplary.