Application of heat treatment to enhance permeability in tight gas reservoirs

During the drilling and completion phases, the primary mechanisms of near-w ellbore formation damage can be attributed to the following factors: 1) pol e throat constriction caused by clay swelling, deflocculation due to incomp atible fluids or clay migration; 2) water blocking resulting in a reduction in relative permeability to hydrocarbons; 3) plugging with drill solids an d mud products; and 4) loading of the reservoir with drilling or completion fluids. In tight reservoirs, phase trapping and water-blocking are believe d to be the primary causes of near-wellbore formation damage, resulting in very low productivity. Clay swelling and phase trapping in tight gas reserv oirs during drilling and completion have long been identified as major prob lems. Preventive measures have been discussed in literature; however, preve ntion of clay damage and phase trapping is not always possible or effective and curative measures may then become necessary. Several curative methods have been attempted and presented in literature with mixed success. A formation heat treatment (FHT) process has been developed in the last fou r years and initial field test results showed promise. The primary mechanis ms of the FHT process are to vapourize blocked water, dehydrate clay-bound water, destroy clay lattices and possibly create microfractures due to ther mally induced stresses, with the objective of removing near-wellbore drilli ng induced skin damage. The objective of this laboratory study was to evaluate the feasibility of a pplying the formation heat treatment process on cores taken from a tight ga s reservoir. The results indicate that the FHT stimulation at 649 degrees C resulted in a 210% improvement in permeability from the baseline undamaged value and 675% improvement from the damaged (water-trapped) value. The pos t FHT waterflooding of the core still showed 50% improvement in permeabilit y from the baseline value and 275% more than the water-trapped value, Labor atory results along with the field logistics are presented in this paper.