Technologies

The diffracted component of the seismic field carries much less energy than the reflected component and requires a special technology for its effective extraction. “PetroTrace” company has developed and implemented its own technique for extracting the diffuse component based on the three-dimensional Radon transformation, which allows us to successfully separate reflections and diffractions on depth-migrated seismograms in the reflection angle domain. The diffuse component volume resulting from special adaptive pre-stack processing helps to more confidently locate low-amplitude discontinuities, fractures, karsts and other low-dimensional subsoil features. Highlighting and mapping these elements allows you to refine interpretation, improve the reliability of geological and flow simulation models and so make more informed reservoir development and well planning decisions.

One of the tasks that can be solved using seismic exploration for marine surveys is the assessment of geological hazards and risks for engineering purposes. Anomalies in the near surface structure should be taken into account when planning drilling, as they have a potential risk in terms of time and economic consequences for the project, which may occur in case this specific anomaly is not considered during the installation of a drilling platform or during drilling itself.

The company PetroTrace has special tools, technologies, and experience for performing such work. Special processing and interpretation of marine data allow identifying anomalous objects (such as anomalously gas-saturated intervals of the section, lenses of frozen rocks, zones of destruction, post-cryogenic deformations, paleocuts, zones of disjunctive tectonic disruptions, etc.) and classifying them according to their degree of danger.

Special processing of 3D seismic data in the upper part of the section for engineering-geological tasks is performed using procedures that allow preserving the relative amplitude parameters of the seismic field for subsequent structural interpretation and dynamic analysis of data to determine geological hazards in the near surface on the seabed and in the underlying sediments. After the completion of the work on identifying and outlining potentially dangerous elements of the geological section, they are ranked by degree of risk, and a map of geological hazards is compiled for seismic complexes in the near surface, as well as a summary map of geological hazards.

In the oil and gas industry, almost all decisions are made under uncertainty. As in any business, these include price uncertainty, the possibility of regulatory changes, and delays in infrastructure construction. But the most important uncertainty comes from limited knowledge of the actual reservoir structure and hydrocarbon reserves. This uncertainty is often called subsurface uncertainty.

PetroTrace specialists have accumulated great experience in modeling and assessment of uncertainty as well as in risk mitigation in exploration, development and redevelopment projects of oil and gas assets. The approach used is based on creating a representative ensemble of geological and flow simulation models. Such ensembles can be created both for new fields (greenfields) and for fields with a history of development (brownfields). For gas and gas-condensate fields, an integrated reservoir-well-surface model can be used instead of a standalone flow simulation model to account for the limitations of the production gathering network.

Based on the results of the analysis of the ensemble of models, PetroTrace specialists create probability distributions of key project parameters (reserves, production, NPV,IRR, etc.) as well as maps that help "visualize" the spatial distribution of uncertainty. Analysis of these results allows us to propose changes to the project that reduce its sensitivity to uncertainty while maintaining acceptable economic performance.

Three-dimensional flow simulation models are commonly used to design, evaluate and optimize field development. In most cases, they are controlled downhole,  i.e., assuming that whatever gets into the wellbore under a certain condition (usually minimum bottomhole pressure) will be brought to the surface and delivered through the gathering system. Sometimes flow simulation models are "extended" to the wellhead in order  to account for pressure losses in production tubing and for pump operation. In this case, the minimum wellhead pressure is the condition.

In reality, the minimum wellhead (bottomhole) pressure depends on the fluid flow rate in the surface pipeline (well). To take this into account, PetroTrace specialists create and use integrated reservoir-well - surface models, in which at each time step the solution for the underground part           (formation - reservoir) is linked to the solution for wells and surface pipelines. The result is a digital twin of the field, which can be used to solve a wide range of problems, from long-term optimization of the gathering system to selection of the downhole pumps and justification of the optimal well operation modes.

Integrated models can be created and used effectively for both gas and oil fields at different stages of the field life cycle (evaluation, development, production).

Drilling of horizontal wells and sidetracks helps to return wells on stream, allows to produce oil reserves from water-oil and undrained zones, intensifies production from "stagnant" areas, increasing the recovery factor. However, construction of complex wells increases capital investments and, accordingly, the cost of error in the selection and justification of targets, drilling and completion.

PetroTrace specialists have developed and are applying an integrated technology of geological support of horizontal drilling using three-dimensional geological and flow simulation models. This technology implies three types of works connected with each other and performed sequentially:

• Selection and optimization of the well target (and if necessary, placement of a pilot wellbore) on the three-dimensional models taking into account the current state of development, existing technological limitations, key uncertainties and risks.
•  Drilling monitoring and steering to maximize effective horizontal borehole length. This stage uses geosteering technology to promptly recommend adjustments to the drilling direction based on real-time LWD and MWD data.
• Update of geological and flow simulation model based on the results of drilling and operation of newly drilled wells followed by additional optimization of trajectories of next (dependent) wells.

PetroTrace has accumulated vast experience in geological support of drilling in various geological conditions. In the period from 2018 to 2021 alone, we have supervised the drilling of more than 400 wells with a total length of horizontal sections of about 200 kilometers.

Most carbonate and some clastic reservoirs have natural fractures, which can have a significant impact on fluid flow orientation, well productivity and recovery mechanisms during depletion, water and gas injection. PetroTrace specialists use an integrated approach to analyze all available data (seismic, well logs, core data, conceptual geomechanical model, well tests, production logging, drilling records, etc.). If qualitative seismic data are available, coherence, anisotropy and diffracted wave energy attributes are combined, resulting in trends reflecting interwell density (intensity) and azimuth distribution for major fracture systems.

The main tool for building a three-dimensional fracture model is DFN (Discrete Fracture Network) models, which combine seismic trends, borehole data and conceptual geomechanical understanding of fracturing into a stochastic model consisting of millions of interacting fractures belonging to different families. On this basis, key parameters of the double (components of the fracture permeability tensor, porosity of the fracture system, the matrix - fracture transfer coefficient) or single (effective permeability tensor) porosity flow simulation models are calculated.

The obtained flow simulation models are calibrated to the well test data and also history matched. The fracture model can serve as part of an integrated study, allowing natural fracturing to be accounted for in holistic uncertainty modeling.

Seismic monitoring of field development is one of the modern approaches to observe and control the quality of geological activities in the fields. PetroTrace has the technology to perform 4D monitoring of the diffracted component (4D DI monitoring) of the seismic field. Such kind of research is extremely labor-intensive, since it requires complete reprocessing of seismic data according to a special graph, including specific quality control at each stage. PetroTrace successfully performed 4D DI monitoring at one of the offshore fields in Russia, which gave the operator an understanding of the injection, as well as an area view of the changes in the diffraction cube intensity, which was interpreted as growth of artificial fractures.