Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2001-10-04
2003-06-10
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S140000, C507S145000, C507S212000, C507S269000, C507S272000, C507S277000, C507S906000, C507S925000
Reexamination Certificate
active
06576597
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to clay-free aqueous well drilling and servicing fluids, methods of preparation thereof, and method of drilling a well therewith.
The use of fluids for conducting various operations in the boreholes of subterranean oil and gas wells which contact a producing formation are well known. Thus drill-in fluids are utilized when initially drilling into producing formations. Completion fluids are utilized when conducting various completion operations in the producing formations. Workover fluids are utilized when conducting workover operations of previously completed wells.
The new reservoir drilling fluid system set forth in copending patent application Ser. No. 09/806,752 filed Apr. 2, 2001 and further disclosed in the Society of Petroleum Engineer's paper SPE 68965 entitled “A New Biopolymer-Free Low-Solids, High Density Reservoir Drilling Fluid,” hereinafter sometimes referred to as “NBRDF,” utilizes a non-biopolymer, acid- or enzyme-soluble starch derivative that serves both as viscosifier and fluid-loss additive when combined with activated magnesium oxide and a divalent-cation-based brine. The NBRDF shows a unique shear-thinning Theological profile featuring relatively low, high-shear-rate viscosity along with relatively high, low-shear-rate viscosity. This behavior is highly unusual in high-density, brine-based reservoir drilling fluids. A result of this behavior is that effective hole cleaning is provided without generating excessive high-shear-rate viscosities that lead to disproportionate equivalent circulating densities. The NBRDF system is based on the higher density, divalent-cation-containing brines (utilizing CaCl
2
, CaBr
2
, Ca Cl
2
/Ca Br
2
, Zn Br
2
/Ca Br
2
and Zn Br
2
/Ca Br
2
/Ca Cl
2
) in the 10.0 to 17.5 lb/gal density range, containing at least 1.2 equivalents per liter of a divalent cation salt. The total amount of the sized CaCO
3
bridging particles is kept relatively low, 13 to 35 lb/bbl, so that thin, chemically removable filter cakes are produced. The size distribution of these bridging particles is designed according to the ideal packing sequence for optimizing sealing and producing a minimally invading (well productivity enhancing) fluid.
A number of technical advances in the petroleum industry have created cost-effective methods for the exploration and development of deep oil and gas reservoirs. One result of these developments is an increased demand for higher density reservoir drilling fluids (RDF's). However, the density attainable for economically viable, brine-based reservoir drilling fluids is limited under current technology. Some limitations are based on the fact that current biopolymer-CaCO
3
-brine-based reservoir drill-in fluids utilize viscosifiers that are either incompatible with the higher-density brines of require special mixing equipment/techniques and complex formulations. In other cases, the cost of a base brine compatible with currently available biopolymer viscosifiers is such that the final drill-in fluid is priced out of consideration. The invention set forth in copending patent application Ser. No. 09/806,752 filed Apr. 2, 2001 present a newly developed biopolymer-free fluid system that uses conventional high-density base brines to fulfill the density requirement, a low concentration of bridging-solids, and a pre-gelatinized epichlorohydrin crosslinked amylopectin starch which functions as a viscosifier and fluid loss additive to produce an easily blended drill-in fluid with exceptional rheological and filter cake qualities.
Most brine-based reservoir drilling fluid systems used today consists of five primary components: base brine, pH control additive, biopolymer-derived viscosifier, starch-based fluid-loss additive, and bridging particles. Containing no biopolymers, such as xanthan gum or scleroglucan, the NBRDF system uses a pre-gelatinized epichlorohydrin crosslinked amylopectin starch (hereinafter sometimes referred to as “XLAPS”) that fulfills the role of both viscosifier and fluid-loss additive when combined with a divalent-cation-based brine and a highly activated magnesium oxide. This fluid delivers a unique shear-thing Theological profile that provides effective hole-cleaning without generating excessive high-shear-rate viscosities that lead to disproportionate equivalent circulating densities.
The NBRDF is based on the higher density, divalent-cation-containing brines in the 10.0 lb/gal to 17.5 lb/gal density range. Brine-based fluids based on calcium chloride, calcium bromide, and zinc bromide brines provide several advantages. Formulating RDF systems in heavier brines minimizes the solids concentration required to weight-up to a high density. Keeping the solids low results in a lowering of the plastic viscosity. Buoyancy, or the upward pressure exerted by a fluid against particulates in the fluid, reduces the demands upon the viscosifying additives for particle suspension and cuttings removal.
A primary component of the NBRDF is the matrix of sized CaCO
3
particles, the total amount of which is kept relatively low, 10 to 50 lb/bbl, so that thin lubricious, and easily removed filter cakes are produced. The size distribution making up this matrix of CaCO
3
particles is designed according to the ideal packing sequences for optimizing sealing. This approach is designed to minimize formation damage by forming a thin, ultra-low permeability and high durability filter cake on the face of the formation, thereby minimizing fluid and solids invasion into the formation.
The relatively high low-shear-rate viscosities is a significant point of departure between the new NBRDF system and conventional CaCO
3
-biopolymer-based RDF's in high calcium or zinc environments. Most other brine-based RDF's incorporate both a starch and a biopolymer like xanthan or schleroglucan. Inasmuch as most of the fluid's viscosity is only achieved when the biopolymer is added, dispersed, hydrated, and fully yielded, the biopolymer is termed a viscosifier. The starch is termed a fluid-loss additive inasmuch as the formulations without starch seldom have more than marginal fluid-loss-control character.
The new NBRDF system relies solely on the XLAPS to serve both roles of viscosifier and fluid-loss-control agent. This characteristic alone distinguishes the XLAPS as an unusual starch. XLAPS performs well in brines based on CaCl
2
, CaBr
2
, Ca Cl
2
/CaBr
2
, Zn Br
2
/Ca Br
2
and Zn Br
2
/Ca Br
2
/Ca Cl
2
; but in seawater, NaCl-based and NaBr-based brines, XLAPS does not exhibit much capability as a viscosifier.
The NBRDF system is not intolerant of the addition of monovalent cation salts, like NaCl and NaBr, as long as the addition does not dilute the divalent cation concentration below about 1.2 equivalents per liter. Therefore, little or no difficulty is anticipated in drilling through salt.
In the NBRDF at lower densities and even as high as 14.0 lb/gal, higher low-shear-rate viscosities are consistently developed with the addition of small increments of a highly reactive magnesium oxide (HRMgO), a pH control agent, and/or dipotassium hydrogen phosphate. The suggestion that a pH control additive could be contributing viscosity is quite surprising, especially when it is noted that adding HRMgO and/or dipotassium hydrogen phosphate tends especially to enhance the fluids apparent viscosity at 0.0636 sec
−1
shear rate (LSRV), while having minimal effect on the fluid's viscosity at high shear rates.
A further distinction between the viscosifying characteristics of the new NBRDF and conventional RDF's is the ratio LSRV/AV
600
. The commonly used parameter AV
600
is one-half of the 600-rpm reading on a Fann 35 viscometer. AV
600
is thus the apparent viscosity measured at 600 rpm, i.e., at the relatively high shear rate of 1022 sec
−1
. The LSRV/AV
600
ratio is sometimes referred to as the shear-thinning index (STI). This parameter is dimensionless because both AV
600
and LSRV are measured in the same units (cP). A desirable RDF viscosity profi
Dobson, Jr. James W.
Tresco Kim O.
House Roy F.
Texas United Chemical Company LLC.
Tucker Philip
LandOfFree
Method of increasing the low shear rate viscosity and shear... 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 of increasing the low shear rate viscosity and shear..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of increasing the low shear rate viscosity and shear... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3123572