Open hole/cased hole log analysis

In extended reach and horizontal wells, it is critical to maintain borehole quality and stability to ensure efficient drilling and for the running and installation of completions. Categorising the risk of borehole degradation is becoming an important aspect of the well planning process. The quality of the borehole is affected primarily by geomechanical or drilling practices, which can significantly impact the life cycle and completion expenditure/cost of a well. We show examples of how recently available, high-resolution, acoustic logging-while-drilling (LWD) borehole image logs have enabled detailed characterisation of borehole shape to the extent that we can visualise and analyse all contributors to borehole stability. LWD measurements also enable the use of time-lapse logging; comparing images from the first pass with repeated logging runs at later stages in drilling to look for degradation in conditions of the borehole shape. These data can be used for several new or existing applications that can be split into two main categories: 1. drilling hazards – degrading borehole shape profiles, identification of borehole breakout and washed-out sections and 2. completions hazards – cement volume calculations, identification of trajectory and small-scale irregularities that could impair liner placement. These applications use zonation to describe all ranges in borehole trajectory, borehole shape and image artefact features for coding of the well during or shortly after drilling. This scheme is then combined with a geomechanics-centric integrated risk management workflow which provides an improved well planning process by identifying potential drilling and geological risks in each of the planed well sections. Pre-drill risk identification combined with visual verification of the borehole condition enables quick decision making for drilling and potential de-risking of subsequent wireline logging and completions operations, thereby allowing safe, predictable operations with minimal NPT, from drilling to completions. The enabling technology of high-resolution LWD acoustic imaging has made possible the visualisation of borehole shape features in detail previously not possible in either water or oil-based mud systems.

The North Sea Oil and Gas industry counts over 7,800 wells drilled. The industry is now entering an era of well abandonment and decommissioning. Current barrier verification for P&A requires appropriate pressure testing and includes surface and downhole monitoring.

Globally, Spectral Noise Logging (SNL) has been utilized in many thousands of cases to detect fluid movement behind completion tubulars and/or across a cement barriers.

In Nov 2017, full-scale verification tests were conducted at the International Research Institute of Stavanger (IRIS). These tests were conducted in a controlled environment to verify current technology thresholds. These showed the technique validated the cement barrier integrity during pressure tests and can diagnose channeling as low as 9 ml/min behind the casing. The threshold matrix for different cement defect versus pressure and flow rates allowed the usage of the technology to support the positive qualification of the barrier elements (Dave Gardner, 2019).

Utilizing a purpose-built test assembly of standard oilfield tubular and cement with fitted end caps, a series of pressure tests operations were conducted to identify the pressure and associate leak rates in conjunction with the SNL. The results clearly demonstrated that the logging tool can provide evidence of barrier verification over a wide range of well applications. Barrier qualification requires that three conditions are met; firstly, cement behind casing is in place and not displaying a micro-annulus or any form of fluid movement behind pipe. Secondly, that a cement plug holds pressure and there is also no fluid leak and finally natural shale barriers are active and create a sufficient barrier. Currently, technology is in its 10^th generation, and since the IRIS tests have been used in many wells, covering both onshore and offshore oil and gas wells and wells in highly sensitive environmental areas. On each case the logging operations were used to verify well status before and after the barrier establishment via cement squeeze or section milling and, in several cases, clearly, demonstrate that the barrier status remained ineffective, hidden and further remedial work was required.

This paper discusses the downhole passive noise listening and its spectral analysis technique to prove the effective cement barriers are in place. The concept, methodology and its application which have been successfully tested via yard and field tests are presented in this paper.

This paper presents an interdisciplinary approach to the description of tectonic dislocations made on the basis of interpretation of seismic data, petrophysical analysis of well-logging data in horizontal wells, and inversion of a multifrequency propagation tool. Russia’s need to continue expanding the oil and gas business is pushing it to look east for more production and markets. But everywhere it turns there is stiff competition in a world awash in oil and gas. Russia has looked to the east to find more oil and gas, growing markets and investor support, allowing it to shrug off the global slump and trade sanctions.

Moving their directional drillers into their Houston real-time remote operations centers has improved drilling efficiency for two of the top shale producers. This paper presents an interdisciplinary approach to the description of tectonic dislocations made on the basis of interpretation of seismic data, petrophysical analysis of well-logging data in horizontal wells, and inversion of a multifrequency propagation tool. This work presents a systematic geosteering work flow that automatically integrates a priori information and real-time measurements to update geomodels with uncertainties and uses the latest model predictions in a decision-support system (DSS). The use of intelligent software is on the rise in the industry and it is changing how engineers approach problems. A series of articles explores the potential benefits and limitations of this emerging area of data science.

This paper discusses a study undertaken to gain better understanding of nuclear magnetic resonance (NMR) characteristics of volcanic reservoirs with different lithologies. This paper compares the results of gas identification and lithology identification using pulsed-neutron spectroscopy in openhole and casedhole environments. Coring is essential to offshore exploration programs—but sometimes cores are taken from the wrong formation or return to surface in poor condition. One firm thinks it can solve these costly issues with a first-of-a-kind coring device that uses logging instruments that add accuracy and integrity. The rising cost of fracturing offers a significant incentive for finding ways to avoid unproductive rock.

This course is designed for petro physics and reservoir engineers who are involved in formation sampling and testing. To learn about reservoir characterisation using formation testers, to be able to interpret pressure and fluid properties, and to design a successful sampling and testing operation. This class is designed for geophysicists, reservoir engineers and any engineers involved or interested in wireline formation sampling and testing including petro physical engineers, production engineers and testing engineers. There are no special requirements for this course. It is recommended for participants to bring their own examples to contribute to course discussions.

Africa (Sub-Sahara) Sahara Group discovered hydrocarbons in three wells drilled in Block OPL 274, located onshore in Nigeria's Edo State. Olugei-1 was drilled to a measured depth of 4537 m and encountered five hydrocarbon zones, with 33 m of net pay. Oki-Oziengbe South 4 was drilled to a measured depth of 3816 m and encountered 64.3 m of net pay in 13 hydrocarbon-bearing zones. Oki-Oziengbe South 5 was drilled to a measured depth of 3923 m and encountered 91 m of net pay in 19 reservoirs. Sahara Group (100%) is the operator. Asia Pacific Sino Gas & Energy Holdings (SGE) flowed gas (coalbed methane) from its first horizontal well in the Linxing production sharing contract (PSC) in China's Shanxi province.

Santos discovered gas condensate at its Lasseter-1 exploration well in block WA-274-P, located in the Browse basin, offshore Western Australia. The well reached a total depth of 5329 m and was drilled in 404 m of water. Wireline logging has confirmed 78 m of net pay over the Jurassic-aged Lower Vulcan and Plover intervals, between 4880 and 5285 m measured depth. Multiple independent hydrocarbon columns have been detected, including an estimated 250-m column for the Lower Vulcan reservoirs. Multiple hydrocarbon samples have been recovered; initial analysis confirms a condensate-to-gas ratio in the range of 10 to 25 bbl/MMcf.

Africa (Sub-Sahara) Oil samples have been recovered in the FAN-1 exploration well, being drilled offshore Senegal. Elevated gas and fluorescence were encountered in a shallow secondary target, and the presence of oil was confirmed by an intermediate logging program. Oil samples from thin sand were collected by a wireline formation tester for further analysis. The well will be deepened to a planned total depth of approximately 5000 m. Cairn is the operator (40%), with partners ConocoPhillips (35%), FAR (15%), and Senegalese national oil company Petrosen (10%). A drillstem test of BG Group's Mzia-3 well--located in Block 1, offshore southern Tanzania, at a water depth of around 1800 m--reached a maximum sustained flow rate of 101 MMscf/D of natural gas. The Mzia prospect is a multilayered field of Upper Cretaceous age with a gross gas column estimated at more than 300 m.

Africa (Sub-Sahara) Algeria awarded four of 31 oil and gas field blocks on offer to foreign consortiums in its first auction since 2011. Shell and Repsol won permits for the Boughezoul area in the north of the country, while Shell and Statoil won permits for the Timissit area in the east. A consortium of Enel and Dragon Oil was awarded permits for both the Tinrhert and the Msari Akabli areas. Circle Oil's CGD-12 well, located onshore Morocco in the Sebou permit, encountered natural gas at different levels within the Guebbas and Hoot sands. Wireline logging analysis confirmed a net 9.7 m of pay. The first test, over the Intra Hoot sands, flowed gas at a sustained rate of 2.21 MMscf/D through an 18/64‑in. The primary target, the Main Hoot sands, flowed at a sustained rate of 4.62 MMscf/D through a 24/64-in.