A constrained pressure-temperature residual (CPTR) method for non-isothermal multiphase flow in porous media

For both isothermal and thermal petroleum reservoir simulation, the Constrained Pressure Residual (CPR) method is the industry-standard preconditioner. This method is a two-stage process involving the solution of a restricted pressure system. While initially designed for the isothermal case, CPR is also the standard for thermal cases. However, its treatment of the energy conservation equation does not incorporate heat diffusion, which is often dominant in thermal cases. In this paper, we present an extension of CPR: the Constrained Pressure-Temperature Residual (CPTR) method, where a restricted pressure-temperature system is solved in the first stage. In previous work, we introduced a block preconditioner with an efficient Schur complement approximation for a pressure-temperature system. Here, we extend this method for multiphase flow as the first stage of CPTR. The algorithmic performance of different two-stage preconditioners is evaluated for reservoir simulation test cases.Comment: 28 pages, 2 figures. Sources/sinks description in arXiv:1902.0009

A block preconditioner for non-isothermal flow in porous media

In petroleum reservoir simulation, the industry standard preconditioner, the constrained pressure residual method (CPR), is a two-stage process which involves solving a restricted pressure system with Algebraic Multigrid (AMG). Initially designed for isothermal models, this approach is often used in the thermal case. However, it does not have a specific treatment of the additional energy conservation equation and temperature variable. We seek to develop preconditioners which better capture thermal effects such as heat diffusion. In order to study the effects of both pressure and temperature on fluid and heat flow, we consider a model of non-isothermal single phase flow through porous media. For this model, we develop a block preconditioner with an efficient Schur complement approximation. Both the pressure block and the approximate Schur complement are approximately inverted using an AMG V-cycle. The resulting solver is scalable with respect to problem size and parallelization.Comment: 35 pages, 3 figure

Publication of UK NICE Clinical Guidelines 168 has not significantly changed the management of leg ulcers in primary care: An analysis of The Health Improvement Network database.

Background NICE Clinical Guidelines (CG) 168, published in July 2013, recommend specialist vascular referral for all leg ulcers, defined as a break in the skin below the knee that has not healed within two weeks. Aim To examine the impact of CG168 on the primary care management of leg ulcers using The Health Improvement Network database. Methods An eligible population of approximately two million adult patients was analysed over two 18-month periods before and after publication of CG168. Those with a new diagnosis of leg ulcers in each time period were analysed in terms of demographics, specialist referral and superficial venous ablation. Results We identified 7532 and 7462 new diagnoses of leg ulcers in the pre- and post-CG168 cohorts, respectively. Patients with a new diagnosis of leg ulcers were elderly (median age: 77 years both cohorts) and less likely to be male (47% both cohorts). There were 2259 (30.0%) and 2329 (31.2%) vascular service referrals in the pre- and post-CG168 cohorts, respectively (hazard ratio, 1.05, 95% CI: 0.99, 1.11, p = 0.096). The median interval between general practitioner diagnosis and referral was 1.5 days in both cohorts. Patients from both cohorts who were referred for a new diagnosis of leg ulcers were equally likely to receive superficial venous ablation. Conclusions Disappointingly, we have been unable to demonstrate that publication of NICE CG168 has been associated with a meaningful change in leg ulcer management in primary care in line with guideline recommendations

Dawnbreakers

A group exhibition, curated by Juan Bolivar, which brought together a range of mostly London-based artists, to portray a contemporary consciousness affected by a sense of technological paranoia