I started an in-house computational chemistry activity at Schlumberger Cambridge Research several years ago. The work has been very successful: we have used molecular modelling to design cement setting retarders, novel cross-linkers for hydraulic fracturing polymer based fluids, and new scale inhibitors. In each case, molecules have been designed de novo by computer. We have also been able to accurately simulate the water swelling of smectite clays and on this basis propose new organic clay-swelling inhibitor molecules, whilst more recently, we have applied similar computational methods to study layered double hydroxides and their inorganic and organic intercalates.