\n Reservoir protection in well drilling and well completion is one of the most significant challenges that have been connected with the quality of the temporary plugging zone and the recovery value of the reservoir permeability when the foreign water invaded into the reservoir copied with the temporary plugging agents. The regular temporary plugging agents are linked with high demand for the matching rate about the pore throat of formation, effect of a single, and poor environmental performance, etc. which markedly impact the operational efficiency. This work reports the synthesis and characteristic of starch-based degradable water-absorbent resin to protect the layer during drilling. Both degradable and excellent SDTA through introducing the nanometre calcium carbonate composites which used as the rigid core were synthesized, characterized, and revalued with standard methods. After purification, there were some groups including the carboxylic acid group, amide group, methyl group, and S=O which reflected the successful synthesis of the monomers. The composites displayed remarkable salt resistance and calcium resistance with 5% and 0.5% as well as thermal stability of 130°C and degradation rate of 50%, respectively. Results also demonstrated that SDTA composites could make the mud cake structure more compact and exhibit self-adaptive to the formation. The SEM images of mud cake treated SDTA revealed that the mechanism could be base on the collaborative action of the structure compact and holes plugging to form an impressive filter cake which could effectively avert the water molecules invasion into the reservoir. Hence, SDTA composites could be a suitable material as a degradable temporary plugging agent for well drilling and completion.

Synthesis, Characterization, and Performance Evaluation of Starch-Based Degradable Temporary Plugging Agent for Environmentally Friendly Drilling Fluid

Un algorithme servant à résoudre le problème de Sturm Liouville par la méthode de Galerkin dans le cas de l'utilisation des systèmes automatiques de calcul

In this paper we study an identification problem related to a nonlinear parabolic system. This system, called the nonlinear single phase mud filtrate invasion model, arises in the study of the mud filtrate invasion phenomenon and is presented in Boaca and Boaca (2018). Our objective is to determine the minimal value of the oil reservoir permeability starting from the observed values of the mud filtrate concentration at some time T . We reduce this identification problem to a nonlinear optimal control problem. We prove the existence of an optimal control and obtain the optimal condition. The influence of the noisy measurements and some numerical results are also presented.

Identification of the minimum value of reservoir permeability in nonlinear single phase mud filtrate invasion model

Fractured tight sandstone gas reservoirs were characterized with narrow pore throats, developed natural fractures, abundant clay minerals, and local ultra-low water saturation, geologic characteristics make those tight reservoirs inclined to strong potential damages. Drill-in fluid may easily invades reservoirs along fractures due to the long soaking time and an overbalanced pressure differential, causing serious formation damage and affecting the economic and efficient development of tight gas reservoirs. An integrated multidisciplinary method was pursued in this paper to accurately evaluate the damage extent of drill-in fluid to tight gas reservoirs. The techniques involve different drill-in fluid damage evaluation methods including core analysis, well logging interpretation, the numerical simulation, and well testing analysis. Results show that the average permeability damage rate through natural flowback after HTHP dynamic damage of drill-in fluid in matrix samples (68.45%–70.70%) were much higher than of fracture samples (44.37%–52.28%). The calculation results of resistivity logging data show that the average filtration invasion depth of drill-in fluid was 1.25 m and the median cumulative filtration invasion depth was 1.26 m. When the simulated bottom hole differential pressure was 3.5 MPa and the simulated soaking time was 150 h, the filtration invasion depth of drill-in fluid was 1.30 m and the lost circulation invasion depth of drill-in fluid was 6.34 m. Afterwards, taking the permeability damage rate and invasion depth as the bridges, the damage skin factor was calculated through Hawkins formula, and the calculated results were in good agreement with the decomposition of well testing results. Finally, an integrated multidisciplinary and multiscale comprehensive evaluation method of drill-in fluid damage in fractured tight sandstone gas reservoirs was proposed, which can serve as a guide for the drill-in fluid damage evaluation in fractured tight gas formation.

Comprehensive Evaluation Method of Drill-in Fluid Damage in Fractured Tight Sandstone Gas Reservoir - A Case Study in the ZM Formation, Tarim Basin, China

A nonlinear single phase mud-filtrate invasion model

This paper considers the problem of viscous dissipation in the flow of Newtonian fluid through a tube of annular cross section, with Dirichlet boundary conditions. The solution of the problem is obtained by a series expansion about the complete eigenfunctions system of a Sturm-Liouville problem. Eigenfunctions and eigenvalues of this Sturm-Liouville problem are obtained by Galerkin’s method.

On Viscous Dissipation In Newtonian Fluid Flow Through An Annular Cross Section Tube.

We analyze the entropy generation and the Nusselt number behaviour in power-law fluid forced convection through horizontal parallel plates with third kind boundary conditions. We obtain an asymmetric Graetz problem, and we propose a new Galerkin procedure based on a confluent hypergeometric function in order to solve this problem. Numerical examples are presented and analyzed in order to bring to light the specific behaviour of the mean entropy and the Nusselt numbers.

Entropy generation and the Nusselt number in power-law fluid forced convection through parallel plates with third kind boundary conditions

We address an optimization problem related to a diffusive flow in a nonhomogeneous porous medium More exactly, the purpose is to control by a flow parameter an optimal average of the solution in a subset of the domain The state model is degenerate and ill-posed and this requires to develop a technique of optimization for a singular state system

Ioana Boaca

Papers

A nonlinear single phase mud-filtrate invasion model

On Viscous Dissipation In Newtonian Fluid Flow Through An Annular Cross Section Tube.

Entropy generation and the Nusselt number in power-law fluid forced convection through parallel plates with third kind boundary conditions

Optimization of a singular flow in a porous medium