Acidizing sandstone reservoirs is a complex process. If not fully studied, it could lead to formation damage. A combination of HCl/HF has been widely used to stimulate sandstone reservoirs. However, the success rate is low due to the complexity of the reactions involved in this process. These reactions result in potentially damaging precipitation and cause formation damage. The problem is more severe when dealing with Bandera sandstone formations that contain a high concentration of carbonate minerals and clay particles. The purpose of this study is to present and evaluate multi-stage acid injection into the Bandera sandstone cores to remove formation damage. In this study, coreflood experiments were conducted on Bandera sandstone cores (1.5 in. x 6 in.) at a flow rate of 4 cm^3/ min and temperature of 140°F. A mixture of formic acid and HF was used as an organic mud acid. Preflush of hydrochloric and formic acid was employed to remove carbonate minerals. Bandera sandstone cores contain a considerable amount of HCl sensitive clays. So another stage was employed to cover clay minerals and prevent HCl attack on the surface of clay particles. Different clay stabilizers as well as preflush pore volume were examined in this study. At the end, this multi-stage treatment design was tested on a Berea sandstone core to investigate the impact of mineralogy. During each experiment effluent samples were collected. Samples were analyzed using Inductively Coupled Plasma (ICP) and Scanning Electron Microscopy (SEM) to investigate reaction kinetics and chemistry of precipitation. Chemical analysis confirmed incompatibility of HCl with clays in Bandera cores at 140°F. Clay stabilizer CSA showed the ability to prevent HCl attack on the clay particle’s surface. As a result, a coreflood experiment conducted using CSA led to permeability improvement. The result of the coreflood experiment conducted using CSC indicated that this chemical is able to exchange cations with clay particles, however permeability decreased due to an insufficient injection of preflush. As in another experiment, increasing preflush pore volume using CSC resulted in permeability improvement. CSB completely failed to cover clay minerals and permeability decreased drastically at the end of the treatment.

A solid breaker is used to reduce the viscosity of the gel at pH range of 4-5 for in-situ gelled acids with Zr4 cross-linkers utilize. However, the literature survey confirmed that solid breakers caused a premature reduction in the fluid viscosity resulting in a less than desirable productivity. Therefore, an effective liquid breaker that is based on tetrafluoroboric acid was developed. This study was conducted to evaluate this new breaker system under the following conditions: breaker concentration (0-200 ppm), and acid injection rate (0.5-10 cm3/min). The major findings from the performed viscosity measurements and single coreflood experiments can be summarized as follows: the crosslinking of the polymer occurred at a pH value of 1.8. At a pH of less than 2, doubling the breaker concentration did not affect the viscosity of the acid. However, at a pH of greater than 2, the viscosity of acid was reduced by 30 percent. At a breaker concentration of 0 ppm, the appearance of Zr in the core effluent sample was delayed by 0.25 PV compared to the reaction product, while at 100 ppm, Zr was delayed by 0.75 PV. At 200 ppm breaker, no Zr ions were detected in the effluent samples. Additionally, it was observed that as the breaker concentration increased, more Zr remained inside the core, as ZrF4, which is water-insoluble. Increasing the breaker concentration from 100 to 200 ppm reduced the final normalized pressure drop by 50 percent at injection rate of 2.5 cm3/min. Permeability reduction due to gel was reduced by increasing the acid injection rate.

Made available in DSpace on 2014-12-17T14:06:56Z (GMT). No. of bitstreams: 1 AnaCeciliaVN.pdf: 4627476 bytes, checksum: 03aa7ea0e615f64c7e42bf3a39bdd226 (MD5) Previous issue date: 2008-04-25 / Portland-polymers composites are promising candidates to be used as cementing material in Northeastern oil wells of Brazil containing heavy oils submitted to steam injection. In this way, it is necessary to evaluate its degradation in the commonly acidizind agents. In addition, to identify how aggressive are the different hostile environments it is an important contribution on the decision of the acidic systems to be used in. It was investigated the performance of the Portland-polymer composites using powdered polyurethane, aqueous polyurethane, rubber tire residues and a biopolymer, those were reinforced with polished carbon steel SAE 1045 to make the electrochemical measurements. HCl 15,0 %, HCl 6,0 % + HF 1,5 % (soft mud acid), HCl 12,0 % + HF 3,0 % (regular mud acid) and HAc 10 % + HF 1,5 % were used as degrading environment and electrolytes. The more aggressive acid solution to the plain Portland hardened cement paste was the regular mud acid, that showed loss of weight around 23.0 %, followed by the soft mud acid, the showed 11.0 %, 15.0 % HCl with 7,0 % and, at last the 10.0 % HAc plus HF 1.5 % with just 1.0 %. The powdered polyurethane-composite and the aqueous polyurethane one showed larger durability, with reduction around 87.0 % on the loss of weight in regular mud acid. The acid attack is superficial and it occurs as an action layer, where the degraded layer is responsible for the decrease on the kinetic of the degrading process. This behavior can be seen mainly on the Portland- aqueous polyurethane composite, because the degraded layer is impregnated with chemically modified polymer. The fact of the acid attack does not have influence on the compressive strength or fratography of the samples, in a general way, confirms that theory. The mechanism of the efficiency of the Portland-polymers composites subjected to acid attack is due to decreased porosity and permeability related with the plain Portland paste, minor quantity of Ca+2, element preferentially leached to the acidic solution, wave effect and to substitute part of the degrading bulk for the polymeric one. The electrolyte HAc 10 % + HF 1,5 % was the least aggressive one to the external corrosion of the casing, showing open circuit potentials around +250 mV compared to -130 mV to the simulated pore solution to the first 24 hours immersion. This behavior has been performed for two months at least. Similar corrosion rates were showed between both of the electrolytes, around 0.01 μA.cm-2. Total impedance values, insipient arcs and big polarization resistance capacitive arcs on the Nyquist plots, indicating passivity process, confirm its efficiency. In this way, Portlandpolymers composites are possible solutions to be succeed applied to oilwell cementing concomitant submitted to steam injection and acidizing operation and the HAc 10,0 % + HF 1,5 % is the less aggressive solution to the external corrosion of the casing / Comp?sitos Portland-pol?meros s?o promissores candidatos ? cimenta??o de po?os de petr?leo contendo ?leos pesados submetidos ? inje??o de vapor nos campos do Nordeste do Brasil. Assim, faz-se necess?rio avaliar sua degrada??o frente aos ?cidos comumente utilizados em opera??es de acidifica??o. Al?m disso, identificar a agressividade dos diferentes meios hostis ? corros?o externa do revestimento constitui uma importante contribui??o na decis?o dos sistemas ?cidos a serem utilizados. Foram avaliados comp?sitos adicionados de poliuretana em p?, poliuretana em solu??o aquosa, borracha de pneu mo?da e um biopol?mero atrav?s das API Spec. 10, sendo refor?ados com a?o carbono polido SAE 1045 para os ensaios eletroqu?micos. HCl 15,0 %, HCl 6,0 % + HF 1,5 % (soft mud acid), HCl 12,0 % + HF 3,0 % (regular mud acid) e HAc 10,0 % + HF 1,5 % foram aplicadas como meios degradantes e eletr?litos. A solu??o ?cida mais agressiva ? pasta de cimento Portland convencional ? a regular mud acid, que apresenta perda de massa em torno de de 23,0 %, seguida da soft mud acid, com perda de massa de 11,0 % e da solu??o HCl 15,0 %, em torno de 7,0 %. As menores perdas de massa, no entanto, s?o relativas ao meio agressivo HAc 10,0 % + HF 1,5 %, com perdas no patamar de 1,0 %. Os comp?sitos com poliuretana em p? e poliuretana em solu??o aquosa apresentaram maior durabilidade, com redu??o em torno de 87,0 % na perda de massa frente ao regular mud acid. O ataque ?cido ? superficial e ocorre como uma frente de a??o, sendo a camada degradada respons?vel pela minimiza??o da cin?tica do processo de degrada??o, principalmente no comp?sito Portland-poliuretana em dispers?o aquosa, por ser impregnada por pol?mero quimicamente modificado. O fato de n?o haver, de uma forma geral, influ?ncia do ataque ?cido na resist?ncia ? compress?o e fratografia das amostras, ap?s ataque ?cido, ratifica essa teoria. O mecanismo da maior efici?ncia dos comp?sitos Portland-pol?meros frente ao ataque ?cido ? regido por menores porosidades e permeabilidades que a pasta de cimento convencional, menor quantidade de Ca+2, elemento prioritariamente lixiviado para a solu??o ?cida, efeito tortuosidade e substitui??o de massa degrad?vel por massa polim?rica. O eletr?lito HAc 10,0 % + HF 1,5 % foi o menos agressivo ? corros?o externa do revestimento, com potenciais de circuito aberto superiores ? solu??o simuladora dos poros como eletr?lito, +250 mV frente a -130 mV para as primeiras 24 horas de imers?o, mantendo esse comportamento ao longo de, pelo menos, 2 meses de imers?o. Correntes de corros?o semelhantes entre esses dois eletr?litos, em torno de 0,01 μA.cm-2, e valores de imped?ncia total, arcos incipientes e grandes arcos capacitivos de resist?ncia de polariza??o, indicadores de passiva??o nos diagramas de Nyquist, confirmam sua efici?ncia. Assim, comp?sitos Portland-pol?meros s?o solu??es poss?veis de serem empregadas em cimenta??o de po?os de petr?leo submetidos concomitantemente ? inje??o de vapor e opera??es de acidifica??o, sendo a solu??o HAc 10,0 % + HF 1,5 % menos agressiva ? corros?o externa do revestimento ap?s opera??es de acidifica??o

Made available in DSpace on 2014-12-17T14:08:46Z (GMT). No. of bitstreams: 1 PedroTPA_DISSERT.pdf: 2026522 bytes, checksum: 77beea38c42704a86dbc6a2648061f42 (MD5) Previous issue date: 2011-07-04 / Stimulation operations have with main objective restore or improve the productivity or injectivity rate in wells. Acidizing is one of the most important operations of well stimulation, consist in inject acid solutions in the formation under fracture formation pressure. Acidizing have like main purpose remove near wellbore damage, caused by drilling or workover operations, can be use in sandstones and in carbonate formations. A critical step in acidizing operation is the control of acid-formation reaction. The high kinetic rate of this reaction, promotes the consumed of the acid in region near well, causing that the acid treatment not achive the desired distance. In this way, the damage zone can not be bypassed. The main objective of this work was obtain stable systems resistant to the different conditions found in field application, evaluate the kinetic of calcite dissolution in microemulsion systems and simulate the injection of this systems by performing experiments in plugs. The systems were obtained from two non ionic surfactants, Unitol L90 and Renex 110, with sec-butanol and n-butanol like cosurfactants. The oily component of the microemlsion was xilene and kerosene. The acqueous component was a solution of HCl 15-26,1%. The results shown that the microemulsion systems obtained were stable to temperature until 100?C, high calcium concentrations, salinity until 35000 ppm and HCl concentrations until 25%. The time for calcite dissolution in microemulsion media was 14 times slower than in aqueous HCl 15%. The simulation in plugs showed that microemulsion systems promote a distributed flux and promoted longer channels. The permeability enhancement was between 177 - 890%. The results showed that the microemulsion systems obtained have potential to be applied in matrix acidizing / As opera??es de estimula??o s?o opera??es realizadas com a finalidade de restaurar ou melhorar o ?ndice de produ??o ou inje??o dos po?os. Dentre as opera??es de estimula??o, destaca-se a opera??o de acidifica??o, que consiste na inje??o de solu??es ?cidas na forma??o, com press?o abaixo da press?o de fratura da forma??o. A acidifica??o tem como principal objetivo remover danos causados nas etapas de perfura??o e/ou workover, podendo ser realizada tanto em arenitos quanto em carbonatos. Um dos pontos mais cr?ticos da opera??o de acidifica??o ? o controle da rea??o ?cido-rocha, pois a elevada velocidade da rea??o faz com que o ?cido seja todo consumido na regi?o pr?xima ao po?o, fazendo com que o tratamento ?cido n?o atinja a dist?ncia desejada. Dessa maneira, as regi?es com dano podem n?o ser ultrapassadas. Este trabalho teve como objetivo obter sistemas microemulsionados est?veis ?s diferentes condi??es encontradas no campo de aplica??o, avaliar a cin?tica de dissolu??o da calcita nesses sistemas, bem como, simular a inje??o desses sistemas realizando ensaios em plugues. Utilizaram-se sistemas microemulsionados obtidos a partir dos tensoativos Renex 110, Unitol L90 e o OMS (?leo de mamona saponificado). Foram utilizandos o sec-butanol e o n-butanol como cotensoativos. Como componentes org?nicos foram utilizados o xileno e o querosene e como componente aquoso foram utilizadas solu??es de HCl variando-se a concentra??o de 15-26,1%. Os resultados mostraram que os sistemas microemulsionados foram est?veis ? temperaturas de at? 100?C, ? concentra??es elevadas de c?lcio, ? salinidade de at? 35000 ppm e a concentra??es de HCl de at? 25%. A cin?tica de dissolu??o da calcita, ao utilizar os sistemas microemulsionados ?cidos, foi at? 14 vezes mais lenta quando comparada com a solu??o de HCl 15%. Os resultados da inje??o dos sistemas ?cidos mostraram que as microemuls?es favorecem um fluxo mais distribu?do com rela??o ao HCl 15%, bem como, formam canais mais longos, promovendo incrementos na permeabilidade dos plugues de 177 - 890%. Os resultados mostraram que os sistemas microemulsionados possuem potencial para aplica??o em opera??es de acidifica??o de po?os