The MPD Operations Matrix was introduced in 2007 to serve as an operational guide for drilling MPD sections. The intent of the matrix is to balance operational, well, and equipment limitations with 'acceptable' influx volumes. The operations matrix has become the cornerstone of MPD projects worldwide, and is in fact a mandatory component of planned MPD wells in the Gulf of Mexico. In its current format, guideline for use of the matrix include developing criteria to categorize an influx such as its state, rate, duration, and size. Calculating these criteria and populating the matrix with them all can lead to some confusion, and many default to including only an influx size for simplicity, despite the fact that the other criteria can help in characterizing an influx further. Further, the acceptable influx size is most often limited to the detection capability of the MPD equipment, and not what the overall primary barrier envelope can handle.In this paper, a method for calculating acceptable influx volumes is outlined, and the calculation algorithm is adapted to a software tool. The results are displayed graphically in an Influx Management Envelope. The Influx Management Envelope is an evolution of the tabular MPD Operations Matrix, and includes all of the same influx indicator and pressure criteria, but offers a simpler, straightforward operational interpretation of influx limits.The effects of section depth, well geometry and hole size on influx volume limits will also be investigated, and development of a sample Influx Management Envelope is presented.

This paper describes the development of a reliability based design format, Load and Resistance Factor Design (LRFD), for casing used in oil and gas wells. Although LRFD methods have provided a basis for design in a number of industries, it has not been widely applied to the design of casing. Load and resistance factors in LRFD account for the influences in the variability of design loads, steel properties and geometrical tolerances on the casing design for a particular application. These factors are analogous to experience based safety factors in Working Stress Design (WSD). However, they are determined by comparing the reliability estimated design by an explicit consideration of the design uncertainties with the tubular design obtained by the specified design check equations. Historically all wells have been designed using WSD. WSD assumes historically based safety factors in the design process. Little documentation and insight into the degree of safety is allowed with WSD. The LRFD approach considers and quantifies uncertainties, risk, and economics with the well design. With LRFD the engineer selects the level of risk which one wishes to design based on the well?s economics, safety, and environmental concerns. LRFD allows the engineer to treat wells differently. The engineer can take different risk levels based on the well type (exploration versus production)as well as what limit state the engineer is designing for (burst versus collapse). LRFD allows the design to fit the application. Two years ago a commitment was made to a multi-million dollar, multi-discipline quantitative risk assessment based research and development project with the objective of 1) increasing reliability and decreasing down time, 2) minimizing environmental impact, and 3) maximizing well economics for OCTG. This project has been completed, is functional, and is based on the Load and Resistance Factor Design methodology. This overview paper will discuss the limitations of previous methods, the hurdles which were required to be overcome in bringing the LRFD method operational, and the advantages of the new method. INTRODUCTION It is important to realize that LRFD is more than a design philosophy. Material and quality requirements are required to adequately support the design. It does not matter how elaborate or sophisticated a design is, if the material requirements are not met and the quality system is not adequate to support the material requirements, the design will not perform as required. In short, LRFD is a complete package of design, material specifications, and quality systems which cannot be separated. Figure 1 shows how the reliability based design concept is a compete and integrated package. The Design logo shows how load and strength are not deterministic values but are stochastically based. As long as strength is greater than load, no failure will occur. The area of overlap shows the probability of failure. The Material logo shows a failure assessment diagram which is used to determine if the material is acceptable for the given load and well conditions. The third and final logo, Quality Systems, shows the supplier switching rules for assuring good quality material.

This paper describes a reliability based design of drilling casing and tubing in the load and resistance factor design format. The approach is based on the fundamental principles of limit state design. The paper identifies the limit states of pipe performance in well applications, discusses stochastic modeling of the load and resistance variables, and describes calibration of the design check equations. In the calibration analysis, uncertainties in the various design variables, e.g., kick load intensity and steel mechanical properties, are determined from analysis of the field and laboratory data and represented by appropriate statistical distributions. The reliability based design procedures are complemented by the pipe specifications and quality assurance procedures, also described in the paper. Application of the load and resistance factor design of casing is illustrated by an example problem. BACKGROUND Oil country tubular goods (OCTG) are subjected to a variety of loads during their service lives. These loads originate from various operations, e.g., running, cementing or producing, and accidental conditions such as the kick, or lost returns. Variability of the drilling tubular's strength and loads is well recognized [1, 2]1. The strength uncertainty, for example, arises due to the inherent variability of material properties, workmanship, and handling of tubulars during installation. The load uncertainty is associated with a designer's inability to estimate loads precisely. The objective of design is to estimate the "minimum" strength and the "maximum" load over the life of a tubular and make sure that they are separated by an adequate margin. Traditional design utilizes experience based safety factors, along with a characteristic set of loads and strengths, to assure the safety of tubular design. These procedures work well when a large database of experience supports the design. However, outside of the historical experience, or when new materials and novel applications are considered, for example, deep sour wells, the basis of judgment essential to establish a safety factor is lacking. As a result, the safety of these designs cannot be assured to a known extent. A number of other issues question the validity of the traditional approach to produce optimum casing and tubing designs. Exploration and production well designs consider a distinctly different knowledge base for their load estimation. The consequences of failure of as-intended performance are also different for various applications of a given casing or tubing string. Obviously, the safety margin requirements should also vary. Also, the traditional safety factor approach considers the stress at a selected point to be the appropriate design criterion. However, it can be shown that in well design, as indeed in many other structural applications, capacity of a structural member is better characterized by its gross or total failure behavior, rather than the stress at a selected point. This is due to the fact that load bearing capacity and stress are often not linearly related.

The present paper describes the development of reliability-based design criteria for oil and/or gas well casing/tubing. The approach is based on the fundamental principles of limit state design. Limit states for tubulars are discussed and specific techniques for the stochastic modeling of loading and resistance variables are described. Zonation methods and calibration techniques are developed which are geared specifically to the characteristic tubular design for both hydrocarbon drilling and production applications. The application of quantitative risk analysis to the development of risk-consistent design criteria is shown to be a major and necessary step forward in achieving more economic tubular design.

This paper was prepared for presentation at the 1999 SPE/IADC Drilling Conference held in Amsterdam, Holland, 9-11 March 1999.