Decision trees have been used for many years in conventional oil and gas plays to help managers better understand risk and expected value for a project. Although industry has rapidly shifted over the past decade to developing unconventional resources, application of decision trees to these plays has lagged behind. When building decision trees for unconventional plays, it is often unclear to evaluators how to build the tree, namely, how to estimate the probability of meeting a given commercial threshold, as well as the production profiles and costs to use for each branch of the tree. This paper presents a workflow that can be used to build a decision tree for an unconventional play in the appraisal phase of development, given ranges of uncertainty in production profiles and drilling and completion costs. In applying this workflow, managers will better understand both the drivers of uncertainty in expected value and how they can influence it via appraisal program design and setting commercial thresholds. An example from a North American unconventional play is used as an example to illustrate the steps of the workflow.
Risk analysis is a term used in many industries, often loosely, but we shall be precise. By risk analysis, we mean applying analytical tools to identify, describe, quantify, and explain uncertainty and its consequences for petroleum industry projects. Typically, there is money involved. Always, we are trying to estimate something of value or cost. Sometimes, but not always, we are trying to choose between competing courses of action.
In the context of risk, a decision tree is a sequence of nodes which are either a decision or an uncertainty, and outcomes associated with each mode. The purpose of a decision tree is to define the set of scenarios and the sequence of events that guide the evaluation of risk and return. It is displayed as a pictorial device, consisting of nodes and branches, that describes two or more courses of action and the resulting uncertainties with probabilities of occurrence, as well as possible subsequent actions and uncertainties. The solution to the tree consists of a preferred course of action or path along the tree, together with the resulting expected value.
Rabinovich, Michael (BP) | Bergeron, John (BP) | Cedillo, Gerardo (BP) | Mousavi, Maryam (BP) | Pineda, Wilson (BP) | Soza, Eric (BP) | Le, Fei (Baker Hughes, a GE Company) | Maurer, Hans-Martin (Baker Hughes, a GE Company) | Mirto, Ettore (Schlumberger) | Sun, Keli (Schlumberger)
Copyright 2019 held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors. Annual Logging Symposium held in The Woodlands, TX, USA June 17-19, 2019. ABSTRACT Typically, only conventional logging while drilling (LWD) resistivity and gamma ray logs are acquired in overburden sections of deep-water wells. Very important decisions impacting drilling safety and borehole stability must be made based on correct and timely interpretation of these logs. Drilling-induced fractures, faults, and eccentricity effects in large holes drilled with oil-based mud are common reasons for anomalous responses of LWD resistivity tools in overburden sections. These anomalies are often associated with fluid losses and other drilling hazards such as borehole assembly sticking. With the limited number of real-time (RT) measurements even if the optimal minimal set of RT curves is selected, the interpretation of these anomalies is challenging. Drilling-induced fractures can be misinterpreted as eccentricity or even as a permeable zone with resistive invasion in water sands or with a hydrocarbon-bearing layer, which is especially important for proper casing and cementing decisions. Resistivity modelling is an irreplaceable tool that enables us to uniquely identify the cause of each anomaly. Time-lapse measurements also help to recognize and identify the causes of anomalies as borehole conditions change with time. Fractures can become deeper with continued overbalance or healed with lost-circulation material or a reduction of equivalent circulating density. Washouts typically enlarge with time and after reaming. We present several case studies from deep-water wells in the Gulf of Mexico illustrating typical LWD resistivity anomalies in overburden sections. The examples include fault identification and borehole events such as fluid losses, borehole enlargement, and gas-bearing intervals. The challenges of interpreting each anomaly and the necessity of the appropriate LWD resistivity modeling kit are clearly demonstrated. Many of the examples illustrate the advantages of measuring after drilling (MAD pass) logs. INTRODUCTION When drilling overburden sections in deep water wells, the hole diameters are big, open hole sections are long and, typically, the LWD suite is limited to conventional resistivity and gamma ray (GR) logs. Additionally, the limited number of real-time (RT) resistivity curves makes the unique interpretation of resistivity data difficult.
Gupta, M K (Oil and Natural Gas Corporation Ltd.) | Sukanandan, J N (Oil and Natural Gas Corporation Ltd.) | Singh, V K (Oil and Natural Gas Corporation Ltd.) | Bansal, R (Oil and Natural Gas Corporation Ltd.) | Pawar, A S (Oil and Natural Gas Corporation Ltd.) | Deuri, Budhin (Oil and Natural Gas Corporation Ltd.)
This paper discusses a case study of one of the onshore field of ONGC where while processing well fluid, frequent surge has been observed leading to shutdown of the SDVs creating severe operational problems and loss of production. It was imperative to find out the problematic wells/lines located in clusters which contribute for surge formation and mitigation approach with minimum modifications.
A transient complex network of sixty five wells flowing with a different lift mode such as intermittent gas lift, continuous gas lift etc were developed in a dynamic multiphase flow simulator OLGA. Time cycle of each well were introduced for intermittent lift wells. Simulation study reveals pulsating transient trends of liquid flow, pressure which was matched with the real time data of the plant and hence confirms the accuracy of the model. After verifying the results, different scenarios were created to determine the causes of surge formation. After finding the cause, a low cost approach was considered for surge mitigations.
An integrated rigorous simulation was carried out in OLGA, by feeding more than 12,000 data points to obtain model match. Several scenarios were also created such as optimization of lift gas quantity, optimization of elevation and size. Trend obtained after each scenario was pulsating behaviour and it matched with the real time data appearing in the SCADA system of the field. After rigorous simulation with each scenario, it was established that the cause of surge forming wells/pipelines. Once the root cause of surge has been confirmed then quantum of liquid generated due to surge was determined. Adequacy checks of the existing separators were carried out to estimate the handling capacity of the existing separators at prevalent operating condition. After adequacy check it was found that existing separators cannot handle the surge generated in that time interval leading to cross the high-high safety level, resulting closure of shut down valve (SDV). After establishment of root cause of the surge, a low cost solution with small modification in pipelines and control system/valves was adopted to arrest the surges. It was first of its kind simulation carried out for a huge network of wells/ pipelines by feeding more than 12,000 data to analyze the surge formation cause and capture its dynamism owing to wide array of suspected causes. This will help to address the challenges of efficiently reviewing the entire pipeline network while designing new well pad/GGS and will also help to arrest surge by adopting a low cost solution wherever such situation arises.
3D wide azimuth seismic data plays a vital role in fault interpretation, which has significant importance during exploration and development stages. Interpreting faults in 3D seismic data is one of the most time consuming and challenging process especially when dealing with poor quality seismic data. This paper provides a complete workflow and example of its application from seismic pre-conditioning to fault detection and extraction automatically based on published concepts by Dave Hale. With recent advancement in computer technology, multi-threaded algorithms and data driven methodologies, geoscientists can automatically detect and interpret virtually all discontinuities in seismic data in an efficient manner.
This workflow involves random and coherent noise suppression, seismic likelihood attributes generation to enhance the discontinuities, detect faults and extract them from thinned fault likelihood volume. Unlike other fault tracking methods that use local seismic continuity attributes, such as coherency, this automated method incorporates aspects of Hale's fault-oriented semblance algorithm, which highlights fault planes with unprecedented clarity.
This methodology has been successfully applied on complex faulted reservoirs. It contributes to the extraction of detailed discontinuity information (minor and major) from 3D seismic data. The traditional manual interpretation step that follows the detection of faults was time consuming and error prone. Automated fault interpretation improves the fault tracking accuracy, consistency and significantly reduces fault interpretation time in prospect generation. This workflow will optimize and reduce uncertainty associated with the seismic fault interpretation process.
Alkinani, Husam H. (Missouri University of Science and Technology) | Al-Hameedi, Abo Taleb T. (Missouri University of Science and Technology) | Dunn-Norman, Shari (Missouri University of Science and Technology) | Alsaba, Mortadha T. (Australian College of Kuwait) | Amer, Ahmed S. (Newpark Technology Center/ Newpark Drilling Fluids)
As oil prices are fluctuating, decision makers are challenged to make the "best" decisions for field's developments. Decision Tree Analysis (DTA) can help decision makers to make the "best" decisions. DTA focuses on managerial decisions, such as whether to do workover or not, whether the additional information will be valuable or not. The aim of this work is to review the applications of DTA in petroleum engineering and provide a clear methodology on how to apply DTA for any petroleum engineering application.
The combination of Expected Monetary Value (EMV) and DTA is one of the most common methods used in the decision-making process. If EMV is positive, the decision is considered to be feasible. However, that doesn't mean the decision will be successful at all times. It simply means that if a similar decision is made for a larger number of cases, the decision will be successful. DTA will account for the uncertainty in the probability. A good number of papers about the applications of DTA in petroleum engineering were read and summarized into three categories. Also, a clear methodology on how to apply the DTA for any petroleum engineering application was established.
After reading and summarizing a good number of papers and case histories about the applications of DTA in petroleum engineering, it was concluded that the applications can be classified into three main categories; applications of DTA and EMV for the whole oil and gas prospect projects, applications of DTA and EMV for a specific operation or development, applications of DTA, EMV, Monte Carlo simulations, and other methods to assess the value of information. These applications were summarized into tables.
In addition, a clear methodology accomplished by a flowchart that explains how to successfully apply the EMV and DTA for any petroleum engineering application was provided. The method consists of three main steps: 1) how many scenarios need to be considered and what are they 2) collection of the required data 3) use the visual tool (DTA) or programming to find EMV. Each of the previous steps has its own challenges, thus these challenges were addressed and the solutions to overcome the challenges were provided. Finally, practical guidelines have were developed that when used with the accompanying flow chart will serve as a quick reference to apply the DTA for any petroleum engineering application.
As the petroleum engineering applications becoming more complicated nowadays, accomplished by the oil prices fluctuations, the decision-making processes becoming more difficult. The DTA is a very important tool for the decision makers to make the "best" decision. This paper provides a clear methodology on how to successfully apply the DTA which can serve as a reference for any future DTA applications in petroleum engineering.
The objective of this paper is to demonstrate how advancedrealtime monitoring (ARM) utilizing advanced hydraulic and mechanical modelling of the drilling process provided early detection of anomalies by giving diagnostic messages during drilling operations. These achievements can minimize non-productive time and invisible lost time and maximize the benefits and value of operations; if they are utilized to its full potential by operations. Some well cases are used to illustrate the methodology and its results. Among problems diagnosed are losses, stuck pipe during drilling and casing running, downhole equipment leakage and improper hole cleaning. In some cases, action was taken based on the diagnostics; and the operational conditions were modified to mitigate the situation. In other cases, the warnings were not taken seriously, the situation worsened until the problem was irreversible and a stuck situation occurred. In one well presented in the current study a stuck pipe situation happened during drilling 8½" section which led to a downtime of more than 20 days. By utilizing the ARM, it couldhave been possible to detect some early signs of the stuck conditions in the wellbore and avoid it. Another stuck situation in awell during 14-inch Casing running, led to downtime of more than 10 days which involved breaking out the casing above the stuck point and performing P&A. The ARM provided early signs of stuck casing that was about to occur, and these signs first started appearing about 15 hours before the pipe got completely stuck. This paper will present the Advanced realtime Monitoring ARM System and the modelling behind this. Also, the plans for further implementation and integration of this in the work processes will be discussed, before results from the first year of utilization will be presented with examples.
Müller, Nathalie (Fraunhofer-Institut für Windenergie und Energiesystemtechnik (IWES)) | Kraemer, Peter (University of Siegen) | Leduc, Dominique (Research Institute of Civil Engineering and Mechanics (GeM)) | Schoefs, Franck (Research Institute of Civil Engineering and Mechanics (GeM))
A fatigue test has been conducted on a large-scale offshore wind turbine grouted connection specimen at the Leibniz University of Hannover. For detecting damages in the grouted joint, a structural health monitoring (SHM) system based on fiber optic sensor-type fiber Bragg grating (FBG) has been implemented. By extracting the features of the FBG signal responses using the Wigner–Ville distribution (WVD) and one of its marginal properties, the energy spectral density (ESD), it is possible to detect the occurrence and the global severity of the damage. Some information about the local severity of the damage has also been obtained.
The grouted connection consists of the high-performance grout-filled space between the two structural steel components of respectively the sleeve and the pile of offshore wind turbines (OWTs). For monopile OWTs, it is located around the water level between the transition piece and the pile, whereas for jacket and tripod OWTs, it is located just above the seabed, between substructure and foundation pile. While grouted joints for monopiles are exposed to bending moments, grouted joints for latticed substructures (tripods and jackets) are exposed to predominant axial loadings and low torsional moments (Schaumann and Böker, 2005; Schaumann, Lochte-Holtgreven et al., 2010). It is a critical structural part of OWTs. In 2009–2010, engineers reported grouted connection failures causing slight and progressive settlement of turbines. The problem affected approximately 600 of the 988 monopile wind turbines in the North Sea, requiring further investigations concerning the design of the grouted connection (Rajgor, 2012). Since then, two grouted connection designs reducing the axial forces in this area have been recommended by Det Norske Veritas (2014): using a conical grouted connection (first design) or a tubular connection with shear keys (second design).
The operator experienced an unusual casing failure at a producing SAGD (steam assisted gravity drainage) oil well in summer of 2017. The subject well in the Firebag SAGD field of NE Alberta, Canada had operated successfully for over 11 years. Once the problem was identified, the well was shut in to determine the nature of the failure and options for repair and recovery so it could be returned to operation as soon as possible.
Tasks included identifying and isolating the failure, establishing the cause and nature of the failure, and determining viable repair options. Logging diagnostics to measure/image the failure were performed, which included new ultra-sonic logging imaging technology, high-resolution multi-finger caliper logging, a downhole camera run and conventional eddy flux casing inspection log. Historical log data was also reviewed to assess whether the failure evolved over time, or if the mechanism was acute. Once the nature of the failure was established, the optimal repair method was chosen, planned and carried out.
Sophisticated analysis of multi-finger caliper log data, camera images and new technology in the form of an ultrasonic imaging tool for the casing were utilized and are presented. A discussion of potential root cause mechanisms for thermal wells is provided, including a variety of failure modes that could be ruled out. Confidence in the failure mode specific to this well was increased by considering information acquired from multiple diagnostic tools. The nature of the connection failure determined from this process is outlined, along the rationale behind the repair method selected to remediate the well.