Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2002-01-16
2004-06-08
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C175S065000, C210S727000, C210S729000, C507S139000, C507S145000
Reexamination Certificate
active
06746611
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and compositions for removal or inactivation of hydrogen sulphide or soluble sulphide ions from drilling fluids used in drilling wells in subterranean formations. The invention is also applicable to removal of hydrogen sulfide or soluble sulfide ions from other fluids such as fluids in sewage systems and fluids produced from subterranean wells. The advantages of the invention are particularly appreciated with high pH fluids containing polymers.
2. Description of Relevant Art
Drilling a well in a hydrocarbon bearing subterranean formation for the production of hydrocarbons from said formation typically involves use of a drilling apparatus and drilling fluid. The drilling apparatus usually comprises a bit mounted on a string of hollow steel pipe. This hollow pipe is often used to rotate the bit to enable the bit to cut into the formation. The hollow pipe also acts as a conduit for the drilling fluid to be pumped down to the bottom of the hole, from where it rises to the surface via the annulus between the drill string and the borehole wall. The drilling fluid has many functions, one of the most important of which is to convey the cuttings from the bit downhole up to the surface of the well.
Good shear thinning rheology is an important property for drilling fluids. This property is generally achieved in one of two ways by using a dispersion of colloidal clay minerals such as smectite clays, e.g., bentonite, or by using polymers such as xanthan gum or scleroglucan that can be dispersed in aqueous solutions to give shear thinning fluids. Each approach has known advantages and disadvantages, although use of polymers seems to be the modern trend. Systems based on dispersed colloids are susceptible to the effects of dispersing and flocculating agents, whereas the rheology of polymer based fluids is more easily controlled. A disadvantage of many polymers, however, is that, since they are polyols, they are susceptible to crosslinking at high pH by the presence of even a low concentration of multivalent cation, such as iron (III) ions.
In drilling some subterranean formations, and often particularly those bearing oil or gas, hydrogen sulphide accumulations are frequently encountered. The drilling fluid brings the hydrogen sulphide to the surface. Such sulphide in the drilling fluid is problematic, as it can corrode the steel in the drilling apparatus and may be liberated into the atmosphere as toxic sulphide gas at the well surface.
Generally, to protect the health of those working with the drilling fluid and those at the surface of the well, conditions should be maintained to ensure that the concentration of hydrogen sulphide above the fluid, emitted due to the partial pressure of the gas, is less than about 15 ppm. The partial pressure of hydrogen sulphide at ambient temperature is a function of the concentration of sulphide ions in the fluid and the pH of the fluid. To ensure that the limit of 15 ppm is not exceeded even for the maximum sulphide concentration that may be encountered in a subterranean formation, the pH of the drilling fluid is typically maintained at a minimum of about 11.5. Also, to prevent the soluble sulphide concentration in the fluid from becoming excessive, action is routinely taken to remove sulphide from the fluid.
A common process for removing sulphide from drilling fluids is by precipitation, usually with a solid zinc compound. Zinc compounds commonly used are zinc oxide and zinc carbonate. These compounds react with hydrogen sulphide to form insoluble zinc sulphide. In insoluble form, the sulphide is relatively harmless (unless the pH falls to acid conditions) and can be removed from the fluid by known separation techniques.
Because these zinc compounds are solids, the reaction rate can be slow, which is especially undesirable when high concentrations of sulphide are encountered or when removal of final traces of sulphide is desired. However, soluble zinc salts can not be used as they hydrolyze at low pH, forming gelatinous hydroxide. While the gelatinous hydroxide would still react with the sulphide, the gelatinous solid would likely interfere with the rheological properties of the drilling fluid. Also, zinc salts behave as acids and tend to reduce the pH of the fluid, increasing the risk of greater emission of hydrogen sulphide into the air.
U.S. Pat. No. 4,242,655 to Carney discloses a soluble form of zinc in a chelated from for use as a hydrogen sulfide scavenger in an oil well. The chelating agents disclosed in U.S. Pat. No. 4,242,655 are low molecular weight hydrocarbon based materials containing acetic or nitrogen functional groups with a stability constant in the range of about 10-16, as described by Chaber Martell in Organic Sequestering Agents. Zinc chelates with a stabilizing constant outside of this range of about 10-16 are said to be either ineffective for removing soluble sulphide ion or to adversely affect the rheology of the well fluid.
Various zinc compounds—both soluble and insoluble—have been used as sulphide scavengers for many years and are generally regarded as an industry standard. However, all zinc compounds have the disadvantage that zinc is regarded as a toxic heavy metal whose discharge must be carefully controlled to protect the environment. When a zinc scavenger is used in the drilling fluid, the cuttings, as well as the residual fluid at the end of the drilling operation, will be contaminated with zinc. Environmental awareness is growing worldwide and discharge of waste containing zinc into the sea or uncontrolled land fill sites is becoming increasingly unacceptable. However, if all zinc contaminated waste from drilling activities had to be directed to special waste disposal sites, many commercial operations would be unviable.
Most other heavy metals which react with hydrogen sulphide to form insoluble sulphide such as copper (both oxidation states), mercury, lead, and nickel, also cause environmental concerns and thus are no more acceptable than zinc.
An exception is iron, a metal, that also forms insoluble sulphide upon reaction with hydrogen sulphide but which is largely free from environmental concerns. Iron salts, however, have been found to be unsuitable as sulphide scavengers because the compounds are not stable in solutions at high pH. At the pH used in drilling fluids, both iron (II) and iron (III) are precipitated as gelatinous iron hydroxide, which would have unacceptable effects on the rheology of the drilling fluid.
Solid Fe
3
O
4
has sometimes been added to drilling fluids in the same way as basic zinc carbonate, but the reaction of the iron oxide is slower than zinc carbonate, particularly at the high pH required for drilling fluids exposed to hydrogen sulphide. The reason for the slower action of the iron compound compared to that of zinc is not fully understood. However, currently available sulphide scavengers based on iron are widely recognized as less efficient and less effective scavengers than scavengers based on zinc. Consequently, the environmentally attractive option has been the less effective option.
U.S. Pat. No. 4,756,836 to Jeffrey et al. teaches using an iron chelate as a downhole hydrogen sulphide scavenger in drilling mud, particularly water based clay muds. This patent discloses chelates of iron with hydroxethylethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). The chelates are said to convert hydrogen sulphide to sulphur. Claimed advantages of this invention are said to be that the iron chelate is regenerated by oxygen at the surface and that the iron scavenges oxygen in the mud stream to cut down oxygen assisted corrosion of the drill stem. This patent further teaches that whether the iron is supplied in the Fe (II) or Fe(III) form, exposure to oxygen at some point in the mud flow changes the form to Fe (III) to prepare the chelate for hydrogen sulphide conversion. Oxygen exposure in an aerated mud pit
Halliburton Energy Service,s Inc.
Hruskoci Peter A.
Roddy Craig W.
Tripp Karen B.
LandOfFree
Method and composition for scavenging sulphide in drilling... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and composition for scavenging sulphide in drilling..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and composition for scavenging sulphide in drilling... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3348600