Algorithm for inversion of resistivity logging-while-drilling data in 2D pixel-based model

Multi-frequency and multi-component extra-deep azimuthal resistivity measurements with depth of investigation of a few tens of meters provide advanced possibilities for mapping of complex reservoir structures. Inversion of the induction measurements set becomes an important technical problem. We present a regularized Levenberg–Marquardt algorithm for inversion of resistivity measurements in a 2D environment model with pixel-based resistivity distribution. The cornerstone of the approach is an efficient parallel algorithm for computation of resistivity tool signals and its derivatives with respect to the pixel conductivities using volume integral equation method. Numerical tests of the suggested approach demonstrate its feasibility for near real time inversion.

MODERN ALGORITHMS AND SOFTWARE FOR INTERPRETATION OF RESISTIVITY LOGGING DATA

The electrodynamics of geological media investigates the interrelations of resistivity logging signals and properties of fluid-containing rocks and creates innovative well logging technologies. Its development is inextricably linked with modern techniques for mathematical modeling and quantitative interpretation of high-precision data. In order to increase the information content of galvanic and electromagnetic logging, we have developed algorithms and software for numerical simulation and inversion of field data. In our study of the Cretaceous and Jurassic deposits of West Siberia, a quantitative interpretation of high-frequency electromagnetic and lateral logging signals was carried out. To create geoelectric models, we interpreted the field resistivity logging data by an unconventional quantitative technique based on their joint numerical inversion and estimations of the vertical resistivity of permeable deposits. Another line of our research was aimed at a scientific substantiation of a new technology for mapping and spatial tracking of lateral heterogeneities and oil-promising zones in the Bazhenov Formation. The aim was achieved by using the TEM sounding data on a spatially distributed system of directional and horizontal wells.

Implementation of Vendor-Independent Stochastic Inversion for Improving Quality and Efficiency of Well Placement on the Field of Novatek Company

The article describes the application of a new stochastic inversion of the deep-azimuthal resistivity data, independent from the tool vendor. The new model was performed on the data from several wells of the PAO «Novatek», that were drilled using deep-azimuthal resistivity tools of two service companies represented in the global oilfield services market. This technology allows to respond in a timely manner when the well approaches the boundaries with contrasting resistivity properties and to avoid exit to unproductive zones. Nowadays, the azimuthal resistivity data is the method with the highest penetration depth for the geosteering in real time. Stochastic inversion is a special mathematical algorithm based on the statistical Monte Carlo method to process the readings of resistivity while drilling in real time and provide a geoelectrical model for making informed decisions when placing horizontal and deviated wells. Until recently, there was no unified approach to calculate stochastic inversion, which allows to perform calculations for various tools. Deep-azimuthal resistivity logging tool vendors have developed their own approaches. This article presents a method for calculating stochastic inversion. This approach was never applied for this kind of azimuthal resistivity data. Additionally, it does not depend on the tool vendor, therefore, allows to compare the data from various tools using a single approach.

Novel Integrated Approach for Complex Carbonate Reservoirs Testing with Wireline Formation Tester: Yurubcheno-Tokhomskoye Field Cases Study

In the presented paper, the object of the study are carbonate rocks of the Riphean and clastic-carbonate rocks of Vendian-Cambrian ages, uncovered by the well drilled at Yurubcheno-Tokhomskoye field. These reservoirs are characterized by extremely low porosity (1-4%) and determining saturation nature and fluid contacts cannot be reliably solved by conventional wireline petrophysical logging. Solutions to these problems are provided by interval testing using wireline formation evaluation testing tool (WFT). However, to obtain quality results from WFT testing it is important to identify porous intervals first by using advanced wireline logging services which are sensitive to porosity and fractures. In order to select the optimal WFT toolstring combination and to prospective testing intervals, advanced petrophysical wireline logging suit ran first. Porous reservoirs were identified from density, neutron and nuclear magnetic resonance evaluation. Saturation evaluated through dielectric and induction-based resistivity logging. In fracture-vug type reservoir, the main inflow of formation fluid into the well is provided from fractures, so it was very important to allocate conductive fractures to plan test intervals for WFT accordingly. based on imagers evaluation, fractures and faults were visualized; using Stoneley's wave conductive fractures, not clogged with drilling mud solids were identified; borehole acoustic reflection survey was used to segregate large fractures that propagated in the reservoir; During WFT logging, a total of 23 intervals were tested, for 8 of which reservoir fluid inflow was achieved, in all others, mainly with low porosity or single non-conductive fracture, the inflow was not achieved or was insignificant. According to the results of WFT testing, the nature of saturation for clastic-carbonate sediments of Vendian age was determined. Inflow of formation fluid (oil and water) from Riphean fractured reservoirs was achieved from 6 intervals, with identified fractures according to described above advanced logging suit. In addition, pressure transient analysis was performed, to measure the formation pressure, define pressure gradient curves and assess the fluids contact level with high confidence, for the first time for this field.

Propogation LWD Tool Analysing for Better Saturation Estimation in High Angle Horizontal Well Conditions

Multidepth electromagnetic logging tool is considered as traditional measurements of formation resistivity estimation while drilling. When considering data in wells with high angles trajectory, more than 70 degrees, the resistivity measurements could be affected by several factors associated with geological conditions and logging tool specifications. As the result, during water saturation estimation formation properties could be distorted, which will lead to significant effect of reservoir properties assessment and the design of the horizontal well completion. Within the framework of this paper, various methods of influence on the resistivity readings will be considered, especially with cross boundary effects and reservoir formations with anisotropy. At the same time, propagation resistivity logging technologies while drilling with interpretation and boundary propagation technologies will be observed, which has tilted azimuthal oriented receivers for geosteering service of horizontal wells and additionally helps with take into account of boundary enflurane on standard resistivity logging.

Exploration of Hidden Hydrocarbons in Old Wells Magid Field - Sirte Basin, Libya

It is increasingly important to improve field productivity in today's competitive market. One way to achieve this, is to add new wells which are expensive and time consuming. The other alternative is to identify bypassed hydrocarbons, track changes in saturations and detect movement of reservoir fluid contacts from existing well bores already in place. It is considerably more cost effective and often more environmentally friendly to explore for those hidden hydrocarbons in old wells rather than drill new wells. As the field matures, there is a need to reevaluate the formation in older reservoirs and to focus the development strategy and approach on bypassed oil pockets and depletion levels in producing intervals. The ability to acquire essential logging data behind casing adds a new dimension to cased hole formation evaluation for locating and evaluating potential hydrocarbon zones in a mature field as in Magid field. A basic petrophysical evaluation was performed incorporating the data recorded behind casing by applying {Cased Hole Formation Resistivity Logging (CHFRL)} in each of these wells. Based on the analysis of cased hole formation evaluation results. The un-depleted intervals were commercially exploited adding reserve to the asset. Keywards: Hydrocarbon zones, Majid Field, Sirte Basin, Libya, CHFRL

APPLICATION OF CONVOLUTIONAL NEURAL NETWORKS FOR RESISTIVITY LOGS PROCESSING AND NON-ITERATIVE EXPRESS-INVERSION IN COMPLEX RESERVOIR ENVIRONMENTS

The work is devoted to the development of techniques and software for the quantitative interpretation of resistivity oil well logs. The article considers the results of applying the neural network approach to the processing of resistivity logging data measured at intervals composed of thin layers with contrasting electrical properties. The proposed algorithms combine the advantages of data interpretation based on a two-dimensional axisymmetric medium model and high performance, which allows them to be used at the primary processing stage, increasing the reliability of express interpretation.

A NEW LOOK AT THE DUAL DEPTH OF INVESTIGATION OF LWD PROPAGATION RESISTIVITY LOGGING

It is well established that phase shift and attenuation measurements acquired by an electromagnetic propagation tool come with different depths of investigation (DOI). The attenuation measurement sees deeper into the formation than the phase shift measurement. This difference has been reported not only for the 2 MHz propagation resistivity tool, but also for the deep propagation tool that operates at 25 MHz. Although the difference has been demonstrated with modeling, test tank experiments and logs, a complete physical explanation has been notably absent since the introduction of the MHz-frequency propagation logging in 1980s. The question is so intriguing that it has been raised repeatedly over the past decades: what drives the difference of DOI for the two measurements that are acquired with the same electromagnetic field? In this paper, we revisit this problem with an aim of providing a physical insight to bridge the gap between theory and application. This is an extension of our recent work on the theory of apparent conductivity for propagation measurements. We address the problem by applying high-order geometric theory for low-frequency electromagnetic problems in lossy media in conjunction with the Taylor series expansion for the voltage ratio measured by a propagation tool. In so doing, we find that in a resistive formation where the dielectric effect is small: 1) the phase shift measurement is primarily due to the first-order eddy current induced in the formation; 2) in contrast, the leading source of the attenuation measurement is the second-order eddy current. Since the second-order eddy current is more spread out than the first-order eddy current, this explains why the DOI of attenuation resistivity is larger than that of phase shift resistivity. The difference in spatial distribution of two eddy currents is also the reason for the difference of vertical resolution between the two. The same root cause for the difference of DOI and vertical resolution also holds when comparing R-signal and X-signal from induction resistivity logging. Other properties shared by propagation and induction resistivity logging will be discussed, such as skin effect and dielectric effect, as well as their asymptotic properties in high-resistivity formations. We conclude that propagation and induction resistivity logging are essentially similar, even though the two measurement principles may seem rather different.