Estimación del AOF (Absolute Open Flow) del Reservorio.Simulación de Reservorios Estimación del AOF (Absolute Open Flow) del Reservorio The absolute open flow (AOF) potential of a well is the rate at which the well would produce against zero sandface back pressure. It is used as a measure of gas well performance because it quantifies the ability of a reservoir to deliver gas to the wellbore. Deliverability tests make possible the prediction of flow rates against any particular back pressure, including AOF when the back pressure is zero. This result is illustrated on the following inflow performance relationship (IPR) plot. 1. Types of Deliverability Tests. There are a number of tests which can be conducted in order to calculate the deliverability of a well as described below. 1.1. Conventional Back Pressure Test The conventional back pressure test is conducted by flowing a well at different rates. Each rate is sustained until the radius of investigation has reached the outer edge of the drainage area and pressure stabilization has been reached. This type of test is not practical for low permeability reservoirs because the time to reach pressure stabilization for each rate is excessive. 1.2. Isochronal Test A fundamental reason that the conventional test is theoretically sound is that the radius of investigation is constant for each flow period. In order to uphold this principle, the isochronal test takes advantage of the fact that the radius of investigation is a function of time and not flow rate. An isochronal test is conducted by flowing a well at several different flow rates for periods of equal duration, normally much less than the time required for stabilization. A shut-in, long enough for the pressure to reach essentially static conditions, is performed between each flow Docente: Ing. Darío Cruz 1 Docente: Ing. Simulación de Reservorios period. In tight reservoirs the length of time required to reach pressure stabilization between flow periods could make the isochronal test impractical. 2. They require an estimate of the degree of turbulent flow in the formation. Many tests. should be of the same duration as each flow period. Stabilized Shut-in. This estimate is often based on information provided by other wells in the same formation or calculated from reservoir and fluid properties. 2. Single point tests do not include the multirate portion of a test and consist of only an extended rate and pressure. Darío Cruz 2 . the stabilized shut-in pressure is a pressure that reflects the average reservoir pressure at the time. rather than being long enough to attain essentially static conditions. An extended flow and stabilized shut-in are still performed at the end of these deliverability tests so that the buildup data can be analyzed and from that the stabilized rate calculated. In addition. the stabilized pressure and flow rate point is the extended flow point. In these cases. 1. 2. Stabilized Flow. Normally an isochronal test includes one flow rate that is extended to stabilization and a stabilized pressure and flow rate point is determined. is required. Stabilized flow can be determined by calculation or by creating a model of the reservoir. an extended flow rate. 1. It is either measured during the test or determined from the interpretation of the data.2. 2. it may be possible to flow the well until stabilization during the extended flow period of a deliverability test. In high permeability reservoirs or wells with small drainage areas. are not flowed to stabilization because of time constraints (especially in tight reservoirs). Extended Flow.1.4. however. long enough to reach pressure stabilization. AOF Flow Conditions.Estimación del AOF (Absolute Open Flow) del Reservorio. This point is the extended flow pressure and flow rate for the test. Stabilized generally refers to a test in which the pressure no longer changes significantly with time.3. It also requires an extended flow period.3. For AOF tests. Single Point Test A single point test consists only of an extended flow period. Modified Isochronal Test The modified isochronal test is an isochronal test which requires that each shut-in between flow periods. 3. For both the simplified and LIT analysis. and is often used because it is easier to understand and calculate. where gas viscosity (mg) and compressibility (cg) cannot be assumed to be constant. Pressure Method. in most cases the simplified analysis is sufficient to determine the AOF and deliverability.2. the pressure squared or the pseudo-pressure approach. Simulación de Reservorios doing a forecast at a specified pressure.4. Two types of analysis are available.1. 3. 3. Darío Cruz 3 . Simplified Analysis The simplified analysis is based on the following equation: Pressure squared: Pseudo-pressure: The analysis of a modified isochronal test using the simplified method is illustrated below. especially when dealing with a high pressure system. Thus. 3. 3. 6 months. For the modified isochronal test. 3. However. pseudo-pressure works for all pressure ranges. Pseudo-Pressure Using pseudo-pressure will be more accurate than the pressure squared approach. LIT analysis is more rigorous than simplified analysis and is usually only used in tests where turbulence is dominant and the extrapolation to the AOF is large.Estimación del AOF (Absolute Open Flow) del Reservorio. Types of Analyses. Docente: Ing. However. although it is more difficult to calculate and requires more computational time. Pressure Squared The pressure squared approach is the more traditional method. and finding the point when the rate has stabilized (usually at 3 months. or 1 year) . pws must be used instead of pR because the duration of each shutin period is too short to reach static conditions. the simplified analysis or the laminar-inertial-turbulent (LIT) analysis. it is only valid for medium to low pressure ranges but is just as accurate as the pseudo-pressure approach in this range. two pressure options are available. Docente: Ing. is drawn through these four points. a stabilized point can be found by calculation from a buildup test. Darío Cruz 4 . Simulación de Reservorios The data is plotted on a log-log plot of Dp2 versus qst where Dp2 is defined as: The flow and shut-in periods of equal duration provide the information required to plot four points. A line parallel to the transient deliverability line is drawn through the stabilized point. If the extended flow period does not reach pressure stabilization. This information is used to plot another point called the stabilized point. called the transient deliverability line. The duration of the last flow rate is extended until the pressure response has stabilized. This is called the stabilized deliverability line. A straight line.Estimación del AOF (Absolute Open Flow) del Reservorio. and n is called the inverse slope. C. The other parameter. Docente: Ing. slope is equal to 1 / n.g. In theory. Darío Cruz 5 . the stabilized point) as follows: Note that C and n are considered to be constant for a limited range of flow rates. it is expected that this form of the deliverability relationship will be used only for the range of flow rates used during the test. However.Estimación del AOF (Absolute Open Flow) del Reservorio. in practice it is used indiscriminately for a wide range of rates and pressures. Simulación de Reservorios The parameter n can be determined from the slope of the line as follows: Thus. can be determined using n and the coordinates (qst and pR) of any point on the stabilized deliverability line (e. Docente: Ing. Determinar la productividad optima del reservorio.1. Determinar la distribución del potencial del reservorio. LIT Analysis. Darío Cruz 6 .Estimación del AOF (Absolute Open Flow) del Reservorio. Determinar el Potencial AOF del Reservorio. Determinar el nivel de referencia o Datum. 1. The analysis of an isochronal test using the LIT method is illustrated below. The LIT analysis is used with dealing with high rate wells where turbulence is a major factor. Calcular las constantes C y n del método de Fetckovick para cada pozo. Objetivos. LIT analysis is defined by the following equation: Note that the pseudo-pressure squared terms (a qst and b qst2) are equivalent to skin due to damage (sd) and skin due to turbulence (sturb). 1. The coefficients a and b are defined in the example below. Realizar la corrección de presiones al nivel de referencia. Objetivos Específicos. Only the pseudo-pressure approach can be used in this situation since pressures are in a higher range due to the turbulence effects. Simulación de Reservorios 4. 5. Procedimiento para la estimación del Área de la Estructura mediante el Sistema de Grillado o Mallado.2. 1. Objetivos Generales. Determinar la distribución optima del reservorio. 8 53. Darío Cruz 7 .49 0 0 0 0 0 Docente: Ing. Obtener “C” y “n” promedio.49 23.75 5780 5420 5200 4850 3880 6862 6771 6723 6667 6540 12. Simulación de Reservorios Para la realización de la presente práctica dispondremos de la siguiente información: El plano estructural del reservorio con el que se cuenta es el siguiente: 20/64 24/64 28/64 32/64 40/64 6.21 17. 2.52 24.5 54.17 27.52 13. Obtener el AOF del Reservorio.05 12 4.Estimación del AOF (Absolute Open Flow) del Reservorio.5 52 24.6 53.65 34.74 22.79 24.75 13.82 20. Información. Determinar el AOF de cada pozo.87 303 364 543 658 854 53. 89 25.7 3.3 2.8 Docente: Ing.48 409 660 1025 1176 52.40 24.9 12 11.11 52.5 2.7 2.4 409 673 868 1101 1459 503 53.22 24.1 26.5 2.1 NM 52.4 49.0 NM 3.2 52.52 26.9 5500 5372 5141 4625 4022 3601 7035 6921 6732 6356 5925 5639 14 17.01 2. Simulación de Reservorios YIELD 24/64 28/64 32/64 40/64 48/64 52/64 15.Estimación del AOF (Absolute Open Flow) del Reservorio.11 25.6 52.17 41.0 4.7 28.2 1.5 37.18 45.1 3.1 52 51.9 11.1 60 19.32 25.4 376 475 644 868 1035 1150 54.21 24.6 24/64 32/64 40/64 44/64 24 15 15 52 5811 5730 5527 5428 7025 6921 6722 6630 14.8 51 49.92 26.9 25.7 47.1 50.2 2.2 42.91 3.28 24.24 25. Darío Cruz 8 .6 34.2 27.1 52.86 2.5 24/64 32/64 40/64 48/64 52/64 28/64 24 12 12 12 14 24 5627 5438 5155 4751 4297 5587 7101 7052 6998 6930 6851 7088 16.6 3.2 11.1 53 53.9 24.21 22.47 23.48 26.24 24.0 3.4 2. de la siguiente manera: Pr2 AOF Docente: Ing. mediante el ajuste de los puntos obtenidos en la prueba de producción para cada pozo. Para obtener el AOF de cada pozo tenemos que tomar en cuenta que Pwf = 0 psi. por lo tanto: qg C Pr 2 Pwf 2 Pwf 0 AOF C Pr 2 n n Don de la lectura del AOF podemos realizarla de forma gráfica. 3. Darío Cruz Log(q) 9 . PSI C = Índice de flujo n = Índice de turbulencia n Y “C” y “n” son obtenidos tanto de forma gráfica como analítica. Herramientas y/o Ecuaciones a Utilizar.Estimación del AOF (Absolute Open Flow) del Reservorio. PCS Pr = Presion estática de reservorio. Simulación de Reservorios Para el cálculo del AOF utilizaremos el método propuesto por Feitkovich. PSI Pwf = Presión de fondo fluyente. el cual nos dice que para cada pozo: qg C Pr 2 Pwf 2 Donde: Qg = Caudal de gas. Simulación de Reservorios Y el cálculo de C y n lo podemos hacer mediante el ajuste de los puntos realizados previamente de la siguiente manera: n C log q 2 log q1 log P 2 log P1 qg Pr 2 Pwf 2 n Pwf 0 AOF C n Pr 2 Para calcular los índices C y n para todo el reservorio Feitkovich propone el siguiente método de C y n promedio para el reservorio con los datos de las 4 pruebas o más realizadas a los pozos: q1 (105 ) C (105 ) n q1 (106 ) C (106 ) n _______________ qtotal q2 (105 ) C (105 ) n q2 (106 ) C (106 ) n _______________ qtotal q # datos n C _ _ q # datos log qt (106 ) log qt (105 ) log 106 log 105 qt (106 ) _ (106 ) n 3.Estimación del AOF (Absolute Open Flow) del Reservorio. Corrección de las Presiones de Prueba. luego Docente: Ing. para poder realizar nuestro mapa isobárico se debe llevar todos nuestros datos hacia un nivel de referencia o DATUM. Para esto realizamos la proyección de los pozos 1 – 2 – 4 que se encuentran sobre un mismo eje y podemos realizar la reconstrucción de nuestro anticlinal y haciendo pasar por el centro de gravedad del mismo un recta horizontal obtenemos nuestro Datum. Darío Cruz 10 . Los datos registrados en cada una de las pruebas que tenemos fueron hechos a diferentes profundidades.1. Darío Cruz 11 . Probador DATUM DATUM Docente: Ing. Simulación de Reservorios realizamos la conversión de las presiones encontrando un P para cada pozo con la gravedad específica del mismo.Estimación del AOF (Absolute Open Flow) del Reservorio. Determinar la productividad optima del Reservorio. 6.. Conclusiones. 8. CONSTRUCCION DE LOS PLANOS ISOS Utilizaremos 2 modelos Productividad Optima. PLANILLA DE CÁLCULO El formato que se utilizará se deja a consideración debido a las variaciones existentes en la presente práctica: 7. Para la resolución del problema se construirá una Grilla Ortogonal de dimensiones 2x 2 cm a una escala de 1cm = 50000 mts.AOF.De igual manera se generara 1 mapa isopaco de todo el campo. 9. cálculos aproximaciones y cada detalle que vean conveniente. Resultados.. Esta sección deberá contener todas las gráficas de grillas utilizadas para todos los sistemas de grillas o mallas. es decir resultados. Iso – Iso. SELECCIÓN DE INFORMACION Simulación de Reservorios La grafica de volumen equivalente de gas de condensado en tanque será utilizada para determinar el equivalente de crudo a gas mediante su gravedad especifica.En este modelo generaremos 1 mapa isopaco de todo el campo. No obstante los cálculos referidos al cálculo del AOF y cualquier cálculo auxiliar que se realice deberán estar en esta sección. 4. El mapa estructural nos servirá para determinar las alturas de pozos y el nivel del contacto agua –gas 5. Anexos. Darío Cruz 12 . Como se puede apreciar los resultados que mas nos interesan en la siguiente practica son: La determinación del AOF del Reservorio. Iso – Productividad Óptima. Docente: Ing.Estimación del AOF (Absolute Open Flow) del Reservorio. de simulación Iso-AOF. En esta sección deberán hacer todas las consideraciones necesarias sobre la practica.