Development of Selective Acidizing Technology for an Oil Field in the Zechstein Main Dolomite

This paper presents laboratory studies based on which a stimulation technology for an oil field located in the Zechstein Main Dolomite was investigated. A large number of oil wells in the Main Dolomite produce significant amounts of reservoir water. Matrix acidizing using conventional acid solutions in such wells has caused a significant increase in water cut, because of their affinity for water. The purpose of this cooperation between the Oil and Gas Institute–NRI and the Brenntag Polska was to develop an acid treatment technology that would not increase the water cut after acidizing treatment in wells where oil production is accompanied by the production of reservoir water. Therefore, a series of tests were performed, including the selection of a suitable viscoelastic surfactant that was sensitive to crude oil. The contact of the gel of the viscoelastic surfactant fluid with crude oil resulted in the reduction of its viscosity The tests described herein include dissolution/dispersion tests, rheological tests, acid sludge tests, compatibility tests, core flow experiments, and corrosion tests, which allowed recipes to be developed for the preflush, diverter, and acidizing liquid. Then, recommendations were established for using these liquids in matrix acid treatment. A series of treatments performed according to this technology allowed the removal of near-wellbore damage without increasing the water cut.

The composition of acid/oil interface in acid oil emulsions

In well stimulation treatments using hydrochloric acid, undesirable water-in-oil emulsion and acid sludge may produce and then cause operational problems in oil field development. The processes intensify in the presence of Fe(III), which are from the corroded surfaces of field equipment and/or iron-bearing minerals of the oil reservoir. In order to understand the reasons of the stability of acid emulsions, acid emulsions were prepared by mixing crude oil emulsion with 15% hydrochloric acid solutions with and without Fe(III) and then separated into free and upper (water free) and intermediate (with water) layers. It is assumed that the oil phase of the free and upper layers contains the compounds which do not participate in the formation of acid emulsions, and the oil phase of the intermediate layers contains components involved in the formation of oil/acid interface. The composition of the oil phase of each layer of the emulsions was studied. It is found that the asphaltenes with a high content of sulfur, oxygen and metals as well the flocculated material of protonated non-polar oil components are concentrated at the oil/acid interface. In addition to the above, in the presence of Fe(III) the Fe(III)-based complexes with polar groups of asphaltenes are formed at the acid/oil interface, contributing to the formation of armor films which enhance the emulsion stability.

Solid-liquid separation techniques for efficient recovery of P2O5 from phosphoric sludge

Phosphoric acid sludge is one of the prominent problems in the phosphate industry. Its production is co-occurred by large losses of P2O5 that affect the process performance. Management and valorization of this waste is a key issue. For the industrial application in solid-liquid separation, selecting the suitable technique for an efficient separation is a fundamental factor. Most of the separation processes fail because of insufficient development effort in the laboratory phase and misunderstanding of separation objectives. The aim of this work is to deal with the P2O5 losses by studying their recovery from phosphoric sludge using a physical solid-liquid separation technique. Hence, laboratory tests have been conducted using vacuum filtration, centrifugation, and press filtration. The comparison was based on three requirements: the liquid recovery rate for each method, the amount of P2O5 recovered, and the solid content remaining in the recovered acid. Results showed that press filtration gave the higher performance of P2O5 recovery, up to 88, 90%, followed by the vacuum filtration with 69.81%.and then the centrifugation with 80.91%.

Treatment of Phosphoric Acid Sludge for Rare Earths Recovery I

A total of nine polymers were first tested. Correlations between molecular weight and sludge settling rate were identified for three types of polymers with a general trend of higher molecular weight giving a faster settling rate. Among the non-ionic polymers, the medium molecular weight polymer produced the best results (1831.88 ppm). Among the cationic flocculants, the lowest molecular weight polymer resulted in more REEs distribution (2478.81 ppm). It was concluded that the super high molecular weight of anionic flocculants works best for treating phosphoric acid sludge which resulted in REE concentration of 2568.69 ppm. Five co-polymers with different anionic ratio were tested as well. A higher anionic ratio resulted in faster settlement. It was found that the higher was the anionic ratio of the flocculant, the higher was REE concentration in the final solids and the highest anionic ratio polymer resulted in 2999.64 ppm of REE. This trend was attributed to zeta potential change due to addition of the polymer.