Integrated Production Modelling to Accelerate Recovery in a Mature Giant Gas Reservoir

Abstract

Abstract A quick assessment of the merits of various development strategies can be performed by operating companies whilst having a tool at their disposal consisting of all elements of a production system. To fulfil this requirement, an Integrated Production Model (IPM) of a giant onshore gas field in the Indus Basin of Pakistan was developed. This paper aims to highlight the workflow and lessons learnt in development and calibration of the model. It also showcases the utility of such models. The field in this case study consists of a single giant volumetric reservoir containing dry gas fluid. There are more than one hundred production wells and over 300 km of surface pipeline network. This study had two phases, in the first phase, key elements of the production system i.e. reservoir, wells and surface facilities were modelled and calibrated independently. Reservoir is modelled via multi-tank approach wherein each tank represented a different pressure region of the reservoir. Communication between the tanks was modelled through inter-tank transmissibilities. The surface network was broken down into clusters for ease of development and calibration. After completing calibration of the key elements explicitly; individual elements were brought together to form an integrated production system in GAP and the integrated response of the model is matched against the observed performance which completed the first phase of the study. During second phase, the history matched IPM Model is then used for evaluating the impact of potential development activities in forecast mode aimed for increase in the delivery pressure, field plateau extension and reserves acceleration & increment. Development activities include infill drilling, tubing optimization, acid-stimulation, surface de-bottlenecking and nodal/wellhead compression. This allowed for ranking of the development activities based on their impact in an integrated mode. Furthermore, the impact of variable delivery pressure and scheduling of different scenarios was also highlighted. The paper also highlights the limitations of the integrated model requiring the use of assumptions in development and calibration phase, particularly with regards to the subsurface model for accurately predicting water rates. The importance of updating the model as part of routine functions is also deliberated. It was concluded that for making short to medium-term prediction runs and evaluating development strategies, the IPM is an extremely useful tool. It is strongly recommended to develop an IPM early in the field life and plan reservoir management activities & surface network accordingly. The demonstration of the calibration methodology, workflows and development strategies aided with examples in a unique setting provide a renewed opportunity to develop an understanding on developing and maintaining integrated production models.