Integrated 3D sonic, resistivity, and image logs define reservoir

An operator in the Middle East teamed with SLB to optimize wellbore position by integrating 3D resistivity mapping, 3D far-field sonic imaging, and near-wellbore resistivity images into a groundbreaking multiphysics characterization of a complex carbonate reservoir. The reservoir characterization, 30 m around the borehole, delineated the oil/water contact, hydrocarbon pathways, and fracture network distribution.

The operator needed near-real-time reservoir characterization while drilling a horizontal well to optimize its position within the reservoir and stimulate the correct zones. Therefore, a comprehensive understanding—fluid relationships, rock properties, and structural geometry—of the executed trajectory was required. Insight into structural features, including fracture distribution, as well as an updated geological model would enable maximizing hydrocarbon production.

GeoSphere 360™ 3D reservoir mapping-while-drilling service, 3D far-field sonic service, and FMI-HD™ high-definition formation microimager were recommended because of their joint capability to map the reservoir profile around the borehole. The integrated measurements delineate the 3D geobody, including the fluid and structural contacts.Unlike previous-generation resistivity mapping, GeoSphere 360 service’s resistivity maps are visualized in 3D for greater reservoir insights.

Measurements for resistivity and sonic imaging were independently taken. Then, the 3D far-field sonic imaging was directly compared to the 3D resistivity mapping measurements. The interpretation of the far-field resistivity response was linked with the wellbore images to understand the layering and rock composition. Because these measurements were taken independently and then compared, the operator achieved an unbiased interpretation with three main findings.

First, the study found consistency between the sonic and resistivity measurements concerning dip, azimuth, and distance to the caprock for defining the top and bottom of the reservoir. Additionally, the clear acoustic reflection identified the bottom of the reservoir layer, and the changes in resistivity indicated the saturation variation between the oil/water contact and free-water levels.

Second, there was a correlation between the vertical acoustic reflectors running parallel to the well and the lateral changes in resistivity around the wellbore. This correlation was interpreted as natural fractures, density differences between the rock structure, and hydrocarbon flow units.

Third, subtle resistivity contrasts within the caprock coordinated to varying strikes and dips reflected in sonic imaging. These measurements reveal the heterogeneous and anisotropic nature of the caprock.

In a field with complex reservoir architecture (stratigraphy and fractures) and complex fluid relationships, this application demonstrated how the groundbreaking multiphysics integration of 3D resistivity mapping and 3D sonic imaging achieved an unbiased interpretation based on independent measurements to

• characterize reservoir features (fractures, lithology anisotropy, layering)
• validate interpretations in complex geological environments with structures remotely detected away from the wellbore
• understand fluid distribution at the reservoir scale as a function of structural features and stratigraphic elements
• obtain novel input for property distribution and reservoir dynamics as opposed to existing geostatistical methods to model reservoir properties.

Ultimately, the operator achieved a comprehensive near-real-time characterization of the reservoir to effectively optimize wellbore position and stimulation operations.