Apparatus and method for subterranean injection of slurried wastes

A method for disposing of waste material by injection within a geological stratum, comprising the steps of:

• a) selecting an appropriate generally permeable and porous target stratum, said target stratum being overlain by a layer of relatively low permeability strata;
• b) calculating the approximate total available storage volume of the target stratum, based on the approximate average thickness, area and mechanical compressibility of the stratum and the storage capacity according to the formula:
• Storage Capacity=dP/(dV.times.dt)
• where dP=Injection Pressure--Shut in Formation Pressure
• dV=Volume of Injected Material
• dT=duration of shut-in Period;
• c) calculating the optimal injectivity for the formation according to the formula:
• Injectivity=Slurry Injection Rate/(Press.sub.inj -Press.sub.fmt) where Press.sub.inj =injection pressure and Press.sub.fmt =formation pressure;
• d) preparing an at least partly cased injection well extending from the ground surface into said target stratum;
• e) positioning a pressure gauge within said injection well in the region of the base of said well for measuring liquid pressure within said well;
• f) perforating the casing of said injection well in the region where the well traverses said target stratum;
• g) injecting at generally said optimal injectivity a pressurized slurry comprising said waste material suspended in a carrier liquid into said injection well in a series of discrete injection episodes at an injection pressure equal to or greater than the fracture or overburden pressure, said injection episodes separated by interinjection episodes wherein no slurry is injected and said well is shut-in;
• h) measuring the well bottom pressure of the slurried wastes with said pressure gauge on a generally continuous basis during each injection and interinjection episode with said pressure gauge;
• i) terminating said injection when the target stratum is generally fully saturated with slurried wastes, as determined by the amount of wastes injected and the calculated available storage volume;
• said method being further characterized in that the pressure and flow rate of slurry injection during each injection episode is adjusted to maintain a generally steady state pressure level at the well bottom, as measured by the pressure gauge, each injection episode terminating when the well bottom pressure climbs a predetermined amount above said steady state level and each interinjection period terminating when said pressure drops a predetermined amount below said steady state level.