| dc.description.abstract | Unlocking a tight carbonate formation for oil and gas production by multi-stage acid stimulation is a relatively cost-effective method as an alternative to propped fracturing for production enhancement. Depending on whether treatment pressure is below or above the formation closure stress, acid stimulation is basically divided into matrix acidizing and acid fracturing. In this study, practical methodology to evaluate both matrix acidizing and acid fracturing through treatment monitoring is presented respectively.
For matrix acidizing, monitoring and optimizing a matrix acidizing has been achieved by integrating a forward model used in acidizing design for horizontal wells with a real-time monitoring model for skin evolution during the stimulation. The effect of acidizing is described as an overall skin factor change, and productivity improvement is predicted for the treatment. Then the field treatment data monitored on-site was used to estimate the skin response by treatment injection. History matching procedure of design and actual treatment data will be carried out to update near-wellbore and key wormholing parameters. Through sensitivity study, which parameter should be updated is discussed. Finally optimum rate schedule is identified based on updated parameters.
Meanwhile, for acid fracturing treatment, new method for real-time monitoring of acid fracturing, the inverse injectivity vs. superposition time function plot is proposed, subject to the condition that the treatment pressure is above closure pressure after the breakdown. Combining a linear dual-porosity transient slab model with injectivity concept, actual growing cross-sectional area induced by acid fracturing treatment can be monitored in real-time. After production starts, linear flow diagnostic approach with rate-transient analysis provides cross-sectional area flowing from matrix, which is compared with the area induced by acid fracturing during the stimulation. The treatment efficiency provides engineers with additional information as to whether the designed acid fracturing was performed appropriately under the in-situ closure stress field.
A field case example of both multi-stage matrix acidizing and acid fracturing acid in horizontal well are also presented respectively in the study to illustrate the application of the approach developed, and to show the value of the integrated approach to monitor and diagnose acid stimulation in horizontal wells. | en |
