82nd EAGE Annual Conference & Exhibition

The factors controlled reservoir quality in the Bentiu Formation are: 1) sediments depositional processes; 2) diagenetic processes; and 3) burial depth. As a result, the porosity and permeability of the studied samples vary significantly due to these factors. Based on a detailed sedimentological and petrographical analyses, the following general conclusions are made:

• The coarser to medium grained sandstones with lower total clay content have higher porosity and permeability than sandstones with highest clay content, suggesting that clay content is a major control in porosity and permeability.
• Quartz overgrowths, pyrite, siderite and iron oxide together with kaolinite and chlorite are the major cement minerals observed in the studied Bentiu sandstones. These minerals migrate/ disaggregate into pore spaces and throats, thereby causing a decrease in porosity and permeability.
• With increasing the burial depth, the mounts porosity and permeability decrease due to compaction and cementation (quartz overgrowths).

From its initiation to propagation, opening and closing, a fracture is under continuous pressure as a result of coupled hydromechanical and geochemical processes. The combination of these processes, including for example dissolution and precipitation, karstification and shearing, leads to complex fracture surface geometries that resemble anything but the parallel plate representation that is typically assumed in fracture network models to calculate aperture and permeability.

Using a novel workflow for characterizing fracture roughness and aperture from core plugs, we aim to gain new insights into how different mechanical and chemical processes impact fracture roughness and how the resulting fracture surface geometry influences permeability of shear fractures in shales, to assess the leakage potential of natural fractures in CO2 storage site caprocks.

We make use of a digital microscope and python-based image processing and roughness quantification. The roughness parameters are correlated to permeability data to derive empirical relations for fracture flow modelling based on a known mineralogy and bedding orientation. The results are used to populate caprock leakage risk models in a joint industry research project for CO2 storage, but the methodology can also be applied to naturally fractured reservoirs.

Seismic data collected in complex land settings is often two-dimensional (2D). The data is then processed in 2D, and these 2D images are ideally representative of the subsurface beneath the profile. This may not be the case, however, if the subsurface has complicated three-dimensional (3D) structure and lateral heterogeneity, like in fold-and-thrust belt settings. In order to quantify these 3D errors in 2D seismic images, we carried out a synthetic case study using a 3D model based on the Caipipendi block in Bolivia, where a target horizon lies beneath a thrust fault. We compare results from illumination studies and 2D migrated images with predicted errors due to a single thrust fault. Illumination studies reveal that seismic energy can reflect off subsurface boundaries kilometers outside of the crosslines. The target in the crosslines consequently has migrated depth errors of tens to hundreds of meters. The thrust fault explains the majority of the errors, both in the lateral direction perpendicular to the 2D plane, and in depth. Our thrust fault error prediction equations have the potential to correct for errors in a seismic strikeline due to a cross-dipping thrust fault and can be incorporated into uncertainty analysis and risk assessment.

The present paper will focus on a mega single sensor 3D seismic survey, where different environments that needed to be covered. These includes producing oil fields, oil installations, refinery's, cities, farms and construction sites. Due to these changing as well as challenging environments, a safety standard had to be adopted to support vibrator and explosive sources for safe and successful completion of the project. Peak Particle Velocity (PPV) surveys were conducted using the DIN 4150 German Standard as a reference whenever the seismic operation approached to any oil field infrastructure, populated area or any possible vulnerable hazards. A total of 666 PPV measurements were conducted in multiple environments within the seismic survey boundary. Based on these tests a set of optimum possible safety distances were determined to oil installations, residential structures, construction sites and other infrastructures to ensure that the quality of the final seismic imaging is optimized and survey objective is achieved.

In this paper, I introduce a comprehensive machine learning framework that combines the benefits of complementary algorithms. The user can design his/her own workflow through easy combination of a large number of Python libraries. This approach is addressed to many different types of applications in geosciences at variable spatial scale and for different purposes. I discuss briefly two applications: the first is a case of litho-facies classification of well log data; the second concerns the construction of probabilistic maps of oil distribution using multidisciplinary geophysical data.

Great advancement in Distributed Acoustic Sensing (DAS) technique has contributed to its wide application in the borehole seismology for some geophysical purposes, such as structural analysis, parameter estimation and reservoir prediction. Tarim Basin, as one of the most petroliferous basin in the northwest China, has been known for the notoriously deep well conditions, including high pressure and high temperature. In this context, VSP applications are greatly limited by the bearing capacity of conventional geophones. Alternatively, DAS technique displays its superiority in good adaption to complex environment. In order to target oil and gas reservoirs with deep burial and complex features, a Walkaway-VSP technique is employed to confront the undesired well conditions, which is based on joint observation by DAS and geophones. This study first compares VSP data respectively recorded by DAS and geophones, then discusses the processing method, and finally obtains a high-precision imaging profile, which lays a solid foundation for the later comprehensive geological research.

Multi component technology has been used in a number of oil exploration area in China. However, due to the propagation characteristics of the PS-wave, the first arrival wave of the PS-wave data collected is not easy to identify, so the PS-wave static correction processing is a difficult problem in multi component exploration. The traditional PS-wave static correction values calculation is to multiply the PP-wave static correction values by an empirical coefficient, but this method will produce the phenomenon of periodic jump , so it is not accurate. Generally, the P-wave records contain clear information of the first arrival wave and surface waves, and there is a very important relationship between surface wave and shear wave. Therefore a new calculation method of PS-wave static correction by combining first arrival wave and surface wave is presented to improve the accuracy of PS-wave static correction. Applications on real data show very high performance of the proposed method in this paper.

Naturally fractured-caved carbonate reservoirs in China have some distinctive characteristics: developed multi-scale fractures, vugs and caves, no moveable oil in pores, poor reservoir connectivity and much difficult to develop. How to effectively develop this kind of reservoirs is a major challenge. This paper presents the corresponding development strategy optimization for different reservoir patterns of this kind of reservoirs.

Based on understanding of geological study and dynamic characterization, typical reservoir patterns are identified and established. Corresponding different reservoir simulation models are built for different reservoir patterns. Then reservoir simulation are used for the development strategy optimization for different reservoir patterns. Finally, the optimization results are applied to the enhanced oil recovery of a fractured caved carbonate reservoir in China.

This paper has been successfully applied to a heterogeneous fractured caved reservoirs in China, which provides a reliable foundation for the effective development of this kind of reservoir. Also the method can be used for development strategy optimization study of other kinds of carbonate reservoirs worldwide.

A MEMS (Micro-Electro-Mechanical) based 3-C borehole gravity meter is being developed in China for mineral and hydrocarbon exploration. The 3-C borehole gravity meter is composed of a three-axis gravity sensor chip based on deep silicon etching technique, high precision capacitive displacement sensing and weak signal detection circuitry. The gravity sensing chip is a silicon-based integrated spring-mass block system. The silicon wafer is etched by micro-nanofabrication technique to form a high collimation groove. The size of the gravity detecting mass block in the sensitive unit plays a decisive role in the thermal noise level of the instrument. Deep silicon processing technique can produce thicker silicon mass block (500 µm), which can obtain larger mass block in the same area compared with traditional silicon surface processing technique (10–100 µm). The out diameter of the final tool will be 50 mm with 5 μGal resolution, 20 μGal repeatability, 10,000 mGal measurement range, 155℃ temperature and 100 MPa pressure rating. Apart from 3-C MEMS gravity sensor, a 3-C fluxgate magnetic sensor is also added to downhole tool. This allows us to measure both 3-C gravity field and 3-C magnetic field downhole simultaneously, and conduct joint inversion of both downhole gravity and magnetic data.

Well operation accounts for potential geological and technological capabilities is one of the important factors affecting the efficient production of hydrocarbon reserves. The main tool for substantiating the technological efficiency of drilling new wells is a geological hydrodynamic network model of the field of development object. However, the process of creating a development plan is time-consuming, and the result, in certain cases, ambiguous. To address potential well development area in terms of residual oil, new integrated analysis workflow summarized based on the results which directly related to a reliable study of the sedimentation medium, in particular microfacies and various reservoir property data and production behavior of wells. The new workflow includes the following steps: 1. Study a well re-completion potential and idle wells conditions 2. Establish favorable phase areas for static analysis 3. Carry out dynamic parameters with an application of seismic inversion 4. Identify potential sites constrained by seismic, geological studies and initial production of the oil field 5. Provide suggestions in a new well development plan. This workflow has been applied successfully for the selection of potential zones for drilling new wells at the preliminary design stage, before creating a production network for the reservoir site model.