Optimal Design of Surface Facilities Using Well Bore Analysis

Abstract

Abstract Production Well start-up imposes a variety of design and operational challenges; including brittleness due to low metal temperature and hydrate formation. Conventional methodology utilizes simulation software to analyze the low temperature for topside facilities, without considering subsurface facilities. This approach produces stringent / conservative safeguards resulting in expensive low temperature metallurgy and hydrate inhibitor facilities. This paper compares the well start-up analysis methodology and attempts to present opportunities for optimization and cost-effective designs; relevant for the oil & gas industry in the current economic downturn. A detailed analysis of production well start-up, shutdown and cool-down scenarios is required to confirm primarily the material of surface facilities, downstream of the Xmas-tree. The conventional methodology assumes coincident worst conditions for a conservative design. Although intrinsically safe, the results of this approach lead to a relatively costly design. Alternatively, start-up scenario can be analyzed using an advanced simulation tool which utilizes wellbore data to replicate realistic conditions. This simulation calculates the actual production tubing head pressure at shut-in conditions based on reservoir pressure, temperature, composition and the geothermal gradient inside the well string. The conventional approach is based on assumptions of steady state input parameters which do not accurately represent the transient behavior during start-up and shutdown of process facilities. In view of increased drive towards cost effective designs in the oil and gas industry, this conventional rough approach is no longer appropriate. Based on experience of working with different operators in the area of well start-up scenarios, it is observed that Wellbore Analysis is an appropriate methodology that may be used to analyze the different types of production wells. This realistic simulation results in an optimized low temperature calculation at subsurface and surface facilities during start-up, which is a determining factor for material selection for low temperature conditions. It also provides a true picture of formation of free gases, accumulation of produced water and system dynamics under hydrate formation domain during start-up. The results of hydrate formation behavior inside the production tubing and at the production choke can be utilized to finalize hydrate mitigation methodologies. Thus, Wellbore Analysis helps to optimize the design of surface facilities, narrows the gap between actual operation and simulation conditions, assists in establishing recommended start-up procedure for operators and avoids the use of unnecessary expensive low temperature metallurgy. NPCC, a major EPC contracting company, has been involved in many onshore/offshore oil and gas projects and has vast experience in design and construction of wellhead facilities. This paper discusses the approach of transient studies with and without well bore modeling, as well as their impact on the design of surface facilities. It also highlights the benefits of Wellbore Analysis in optimizing the topside design and consequently improving overall project economics.