A recent challenge of drilling a horizontal well in a Ml Sandstone reservoir presented high seismic uncertainty and limited lateral extent; this well is located in the Napo formation of the Oriente basin in Ecuador. The geology in this basin is complicated; most of the reservoirs are formed from a small, stacked-channel sandstone sequence. As a result, well-to-well reservoirs are difficult to correlate because of their limited lateral extent. Horizontal wells placed in this kind of environment generally require adjustments in the planned directional well trajectory and modification of the navigation TVD when required. The primary goal of this project was to maintain the well in the sweet spot of the reservoir to improve productivity. As a final delivery, the structural map of the top of the M1 Sandstone enabled the customer to adjust the seismic information in the zone of influence of the well. A major drilling company assumed the challenge by using a rotary steerable system, proactive logging-while-drilling azimuthal resistivity sensors, and 3D geosteering techniques to place the well in the sweet spot of the reservoir and to ensure the permanence in the sandstone reservoir. The azimuthal deep resistivity sensor can provide a broad quantity of curves with various depths of investigation (DOIs). Having this information as an entry, the geoscientists applied the three logical geosteering phases of model, measure, and optimize. At the modeling stage, the geosteering team selects the appropriate proactive set of variables to transmit in real time, including compensated resistivities at various ranges of investigation, images, and geosignals according to the geology in the area, reservoir thickness, and existing resistivity contrast. The measuring stage begins by obtaining the selected variables in real time with average resistivities that enable the calculations of the distance-to-bed boundary (DTB) using a forward-modeling technique, while real-time images are compared against modeled information for stratigraphycal positioning. During landing, the drilling and geology departments agreed that the reservoir top was 35 ft (10.7 m) shallower than expected. At this point, the directional drilling plan needed to be changed, beginning the optimization stage even before the horizontal section began. The appropriate combination of reactive and proactive logging-while-drilling sensors enabled the well to be placed parallel to the top of the reservoir, maintaining an optimal distance of 1 to 3 ft, with 100% reservoir exposure in the pay zone and no exits. The main objectives of geosteering were achieved. The well produced 6,800 BOPD after an initial estimate of 800 BOPD. The top of the reservoir was mapped, thereby improving knowledge of this zone for future study.

During the drilling campaign in the Tapi field, Ecuador, events of total losses and directional unexpected behaviors were observed. These issues represent a high risk in the operations and required a better understanding of the geological structures. The use of a new Logging While Drilling (LWD) Micro-Resistivity technology was used for the first time in Tapi field, Ecuador to study the geological and geomechanical characteristics of this field in detail.The tool string was run as a penta-combo with a rotary steerable system with the purpose of getting a hole in gauge and consequently a better image quality. The LWD micro-resistivity images tool provided images of the borehole. The interpretation of the Micro-Resistivity Image started showing an average structural dip trend towards NE, identifying a main structural trend of the field.Two post-drill geomechanical models based on wellbore stability were made in the Tapi I and Tapi II wells. Using the LWD micro-resistivity images technology the current geomechanical model was confirmed. Based on the geological information acquired through the image interpretation (natural fractures orientation, breakouts, faults, structural and stratigraphic dips), the geomechanical model uncertainties were minimized.

Low-resistivity pay reservoirs have been described in many basins around the world. Technical information available explains the causes related to hydrocarbon bearing zones, represented by low resistivity values. These causes are mainly associated with mineralogy and complex pore structures. All the wells drilled and produced in the Johanna Este field in Ecuador have met the condition of pay zones with high resistivity values in relation to the well-known water formation resistivity. A step change in the understanding of the main reservoir M1 sandstone occurred after drilling the horizontal well JE34H. The first half of the lateral section was drilled with resistivity values close to water resistivity. Vertical variations in the resistivity were confirmed in the second half of the well, with no lithologic barriers between both zones observed in the logs. The oil production obtained from this well was recognized as a field record, and the first time it was associated with low resistivity values. After an exhaustive review of the available information including LWD electrical logs, the tool functioning, and cuttings description, it was possible to explain the low-resistivity pay within the M1 sandstone reservoir at the mineralogical level. The density-neutron cross-plots used for lithology identification show that the reservoir is mainly quartz with some mineral mixture. The target zone is mainly made up of medium-to-coarse grain with no visible matrix in the composition, showing no evidence of compaction or cement in density-neutron logs. Macroscopic anisotropy was also discarded as the reason for the decrease in the measured resistivity. In addition, structural compartments and preferential pathways for water invasion created by faults and/or fractures were discarded based on the azimuthal density image interpretation. The possible causes for the low resistivity pay were microporosity, presence of disseminated clay, and presence of conductive minerals. Special analysis (cores, magnetic resonance, capillary pressure, SEM) are required in order to understand the mineralogy and porosity distribution. A low-resistivity pay within the M1 has opened a door for future analysis by means of conventional or special open hole and cased hole logs in order to identify reserves that could be bypassed.