Risk Due to Wellbore Instability

Exploration and production as one of the most important parts of the petroleum industry encounters different problems, usually resulting in nonproductive time and additional expenses. The most common and most expensive of them are related to wellbore instability and associated problems. Wellbore instability problems are usually related to drilling operation, but they can also appear during completion, workover, or the production stage of a certain well. The traditional solution for wellbore instability problems is composed from the early recognition of specific wellbore instability problems, the main cause identification and swift response. For more effective solution it is necessary to incorporate wellbore stability and risk assessment in the early phase of well design. This chapter gives one general overview of wellbore instability problems and their causes as well as an overview of actual approaches and methods in wellbore stability and risk assessment.

General Approach to Risk Analysis

Broadly accepted methodology that is implemented in the oil industry when dealing with risks includes as the first step the identification of possible hazards. That is done by gathering information about degree of risk according to working procedures, processes, and individuals involved in the operation of the process. That is the first step in risk management, an iterative process that must lead to the use of proper measurements in the way of protecting people, facilities and environment. The analysis is done based on the combination of probability and severity of undesirable events, and the final consequences. Explanation of basic terms, their interdependence, dilemmas, and methods of risk analysis are introduced. Each method is shortly described with main anteriority and shortcomings. Differences between quantitative methods, qualitative methods, and hybrid methods (the combination of qualitative-quantitative or semi-quantitative methods) are elaborated. The impact, occurrence, and the consequences are at the end compared to risk acceptance criteria concept. The ALARP (As Low as Reasonably Practicable) framework is explained with some observation on the quality and acceptance in petroleum industry. Finally, the human impact on the risk and consequences is analyzed.

Petroleum Industry Environmental Performance and Risk

The petroleum industry holds long- and short-term environmental risks. Besides production fluids, all petroleum industry activities involve either use of fluids, which contain abundant substances, or waste generation, both associated with potential risk to the environment. The principal environmental risk associated with the petroleum industry is the risk of fluid spill/emission to the environment. Although in recent decades the risk analysis methodologies have matured, to date there is still no universally accepted methodology for environmental risk assessment in petroleum industry. In this chapter, the petroleum industry’s environmental incident history and statistics are presented. The environmental impact of the petroleum industry’s activities, its extent, and trends are analyzed. The overview of pollution sources with associated environmental risk is given along with the analysis of the causes and consequences of incidents in the petroleum industry.

Oil and Gas Storage Tank Risk Analysis

Storage tanks are widely used in the oil refinery and petrochemical industry in storing a multitude of different products ranging from gases, liquids, solids, and mixtures. Design and safety concerns have become a priority due to tank failures causing environment pollution as well as fires and explosions, which can result in injuries and fatalities. The chapter illustrates different types of crude oil and oil product storage tanks as well as the risks regarding the storage itself. Considering that the natural gas, in its gaseous state, is stored in underground storages like oil and gas depleted reservoirs, aquifers or salt caverns, and there are numerous publications and books covering the subject in detail, this chapter only illustrates the storage of liquefied natural gas and the risks posed by its storage.

Risk and Remediation of Irreducible Casing Pressure at Petroleum Wells

Oil well cement problems such as small cracks or channels may result in gas migration and lead to irreducible pressure at the casing head. Irreducible casing pressure also termed, Sustained Casing Pressure (SCP) is hazardous for a safe operation and the affected wells cannot be terminated without remedial operations. It is believed that even very small leaks might lead to continuous emissions of gas to the atmosphere. In the chapter, the author describes physical mechanisms of irreducible casing pressure and qualifies the associated risk by showing statistical data from the Gulf of Mexico and discussing the regulatory approach. This chapter also introduces a new approach to evaluate risk of casing pressure by computing a probable rate of atmospheric emissions from wells with failed casing heads resulting from excessive pressure. Also presented is a new method for assessing potential for self-plugging of such wells flowing wet gas as the gas migration channels could be plugged off by the condensate.

Risk Due to Pipe Sticking

A stuck pipe is a common worldwide drilling problem in terms of time and financial cost. It causes significant increases in non-productive time and losses of millions of dollars each year in the petroleum industry. There are many factors affecting stuck pipe occurrence such as improper mud design, poor hole cleaning, differential pressure, key seating, balling up of bit, accumulation of cuttings, poor bottom hole assembly configuration, etc. The causes of a stuck pipe can be divided into two categories: (a) differential sticking and (b) mechanical sticking. Differential-pressure pipe sticking occurs when a portion of the drill string becomes embedded in a filter cake that forms on the wall of a permeable formation during drilling. Mechanical sticking is connected with key seating, formation-related wellbore instability, wellbore geometry (deviation and ledges), inadequate hole cleaning, junk in hole, collapsed casing, and cement related problems. Stuck pipe risk could be minimized by using available methodologies for stuck pipe prediction and avoiding based on available drilling parameters.

CO2 Underground Storage and Wellbore Integrity

Geologic storage is the component of Carbon Capture and Storage (CCS) in which the carbon dioxide (CO2) is disposed in the appropriate underground formation. To successfully inject CO2 into the subsurface to mitigate greenhouse gases in the atmosphere, the CO2 must to be trapped in the subsurface and must not be allowed to leak to the surface or to potable water sources above the injection zone. For the purposes of risk assessment, a priority is to evaluate what would happen if CO2 migrated unexpectedly through the confining unit(s), potentially resulting in undesirable impacts on a variety of potential receptors. One of the main risks identified in geological CO2 storage is the potential for CO2 leakage through or along wells. To avoid leakage from the injection wells, the integrity of the wells must be maintained during the injection period and for as long as free CO2 exists in the injection zone.

Transportation Risk Analysis

Petroleum is transported across the water in barges and tankers, and on land, using pipelines, trucks, and trains. Natural gas is moved, mainly, by pipelines. The most common causes of tanker accidents are: fire/explosions, loading/offloading, structural damage, collision, and grounding. Pipeline accidents are due to: corrosion, third parties activities, mechanical damage, natural events, and operational error. Some of the most commonly applied preventive activities that reduce spills in waterborne transportation are: double-hulled tanker, navigation safety and radio communications equipment, tanker exclusion zone, etc. The pipeline condition can be recorded by using various nondestructive measurement techniques or by chemical analysis of fluid flows. Different types of sensors can be used to locate and determine the size of an anomaly in the pipeline geometry. Mayor methods for detecting leaks are measuring the hydrodynamic parameters or registering abnormal conditions in the fluid flow and detecting phenomena in the immediate vicinity of the pipeline.

Gathering Systems and Processing Facilities Risk Analysis

Gathering system is defined as one or more segments of pipeline, usually interconnected to form a network that transports oil and natural gas from the production wells to one or more production facilities, gas processing plant, storage facility, or a shipping point. There are two types of pipeline networks: radial and trunk system. Produced well fluids are often complex mixtures of the liquid hydrocarbons, gas, and some impurities that can have detrimental effects on the integrity of the gathering pipelines. It is necessary to eliminate most of the impurities before oil and natural gas can be stored and sold. Complexity of the processing facility depends on the treated fluid composition. Environmental impacts during the oil and gas transportation and processing phase will cause long-term habitat changes. To minimize that, it is very important to implement appropriate activities across the designing, construction, operational, and decommissioning phases.

Risk Analysis in the Process of Hydraulic Fracturing

This chapter focuses on risk to the environment from hydraulic fracturing operations, starting with transport of materials and ending when the well is routed to the production facilities. The initial assumption for the fracturing risk analysis is that the well is new and was constructed correctly so that all producible formations are securely isolated behind the barriers of casing and competent cement. The justification for this assumption is that the vast majority of fracturing is the first major stimulation in a well and occurs immediately after completing a new well. Although many well development problems are blamed on fracturing, there are only excluded problems that are real and worthy of the discussion to help define boundaries of the fracturing risk (King, 2012).