Method of subsurface modelling

A method of extracting hydrocarbons from a subsurface reservoir, the method comprising:

• obtaining history data of at least a first parameter over a first period of time, said first parameter relating to a fluid rate within the subsurface hydrocarbon reservoir, said first period of time comprising a plurality of schedule periods, each schedule period having an associated sampled value of the first parameter at a corresponding time;
• attributing a merge error value to plural pairs of consecutive schedule periods, said merge error value representing a magnitude of the error in a merged value of said first parameter over a duration corresponding to a pair of schedule periods being considered, relative to the sampled values for said pair of schedule periods being considered;
• merging the pair of schedule periods which have the smallest error value attributed thereto, and attributing to this merged schedule period a corresponding merged value of said first parameter;
• repeating steps 2) and 3) thereby to generate a new schedule with a reduced number of schedule periods, thereby reducing simulation computation time;
• modelling the subsurface hydrocarbon reservoir to obtain model data relating to the first period of time;
• using the history data described in terms of the reduced number of schedule periods in a history matching process which matches the modelled data with the history data, so as to predict fluid flow properties relating to the first parameter within the subsurface hydrocarbon reservoir;
• and
• using the predicted fluid flow properties to extract hydrocarbons from the subsurface hydrocarbon reservoir.