Patent Application
20110265997
Embodiments of the invention relate to methods and compositions of fluids for use in the oil field services industry. Specifically, embodiments relate to fluids containing polyacrylamide.
The constraints on gas handling capacity have resulted in shutting-in a significant number of high gas-oil-ratio (GOR) wells. In most cases, the workover objectives involve plugging the invaded gas zones to produce from another zone and restore oil production. One major problem in naturally-fractured carbonates is the reduction of the crude oil production due to the water and gas breakthrough. Numerous solutions take into account several parameters for gas shut off treatment design. Some of these parameters are: determination of the type of system that fits best the well-reservoir conditions, treatment volume, average fissure/fracture width and number of fissures to be plugged. However, another problem is the best placement technique for the sealing system in the gas zone.
Few techniques have been developed to address the gas breakthrough in naturally-fractured carbonates, so it is a matter that has yet to be widely discussed and researched.
The main challenges faced for gas and water shut-off treatments include:
Embodiments of the invention relate to a method for treating a subterranean formation, comprising forming a fluid comprising polyacrylamide and a biopolymer and introducing the fluid to a subterranean formation wherein the polyacrylamide and biopolymer are selected to form the fluid with a longer foam half life and a higher viscosity than if only one polymer were selected. Embodiments of the invention relate to a method for treating a subterranean formation, comprising forming a fluid comprising polyacrylamide and a biopolymer and introducing the fluid to a subterranean formation wherein the polyacrylamide does not alter biopolymer crosslinking.
At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation—specific decisions must be made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In addition, the composition used/disclosed herein can also comprise some components other than those cited. In the summary of the invention and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary of the invention and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors possessed knowledge of the entire range and all points within the range.
The statements made herein merely provide information related to the present disclosure and may not constitute prior art, and may describe some embodiments illustrating the invention.
Embodiments of the invention create a seal in the gas producer zone to trap the gas, trying to avoid or minimize the damage in the crude oil producer zone. Foaming a polyacrylamide-based water control system, becomes one of the best alternative to propose. However, as lab testing has shown over time, polymers by themselves are not capable to maintain a stable foam before reaching the setting time of the system.
For that reason, after an extensive number of tests it has been found that the addition of a biopolymer to the hydrated polyacrylamide considerably increases the gel viscosity and the foam half life without affecting the performance of the system before curing.
The polyacrylamide may include polyacrylamide, grafted polyacrylamide, modified polyacrylamide, polyacrylamide hybrids, hydrophobic polyacrylamide, hydrophilic polyacrylamide, acrylamide sodium acrylate copolymer, and/or any combination thereof. In some embodiments, the polyacrylamide is selected for its molecular weight. In some embodiments, the polyacrylamide has a molecular weight of about 5 to about 15 mM. In some embodiments, the polyacrylamide has a molecular weight of about 200 to about 500K.
The biopolymer may include diutan xanthan, guar and/or a combination thereof.
In some embodiments, the biopolymer crosslinking is not altered by the presence of the polyacrylamide. That is, the fluid has similar viscosity or other rheological properties it would have if no polyacrylimide.
In our lab, some tests have been carried out to evaluate the feasibility of foaming the sealing gel system, which surges as one of the best ways for placement of the sealing system in the gas producer zone. The foamed gel consists of a crosslinked polyacrylamide solution—in both the rigid and flowing versions—plus a surfactant, foamed in a mixer at high-shear rate. The foamed gel is created by means similar to those used for aqueous foam generation, where the major difference between foamed gels and aqueous foams is that the external phase of the foamed gel crosslinks, greatly enhancing the mechanical stability of the foam system. According to lab tests, the polyacrylamide maintains the foam stable for short time, so it becomes necessary the addition of a polymer that aids in increasing the foam half life. Through a couple of lab tests, it was found that polymer of different identity such as guar gum is capable of increasing the foam half life by increasing the viscosity of the crosslinked polyacrylamide solution without affecting the performance of the setting time of the system. So far, on the flowing gel, it has been observed that the flowing gel is more robust when the guar gum is added into the crosslinked polyacrylamide solution.
One major problem of gas shut off is the placement of crosslinked polyacrylamide—such as acrylamide sodium acrylate copolymer and a substituted acrylamide polymer gel is ensuring that the gel is injected into and stays in the gas-bearing zone, until set. For this reason, stable foam is required which requires the optimization of the foam half life and foam quality to allow the system to set and prevent it slumping into the pay zone. It has proved difficult to create stable foam using nitrogen with a polyacrylamide fluid and conventional foaming agents. However, by adding a second polymer to the fluid it is possible to greatly increase the foam half life and the viscosity of the polyacrylamide solution. This is considered to be the result of the second polymer (guar or a biopolymer) greatly increasing the low shear apparent viscosity of the fluid. The increased low shear viscosity indicates a synergy between the polyacrylamide and the second polymer (Table 1 and 2).
15′
Foamed fluids comprised of A1 with Diutan gum have a foam half life greater than five (5) hours. The most stable foam being when there is the greatest degree of interaction between the two polymers (
1. 0.7 wt % Duitan gum+0.5 vol % Ammonium C6-C10 alcohol ethoxysulfate surfactant
2. 0.7 wt % Duitan gum+1.0 vol % Ammonium C6-C10 alcohol ethoxysulfate surfactant
3. 0.25 wt % Duitan gum+0.5 vol % Ammonium C6-C10 alcohol ethoxysulfate surfactant
4. 0.42 wt % Duitan gum+0.5 vol % Ammonium C6-C10 alcohol ethoxysulfate surfactant
Laboratory testing on foam has shown that the waring blender is not the appropriate equipment for foam generation since the mixing is not uniform with the highest shear occurring at the bottom of the blender jar. For that reason, a Silverson mixer—L4RT model—was used for foam testing, since a more uniform foam mixture is achieved as the mixer paddle can move homogeneously throughout the foam.
The procedure for the foaming test is shown below:
Gel Mixing
Foaming Testing in the Laboratory
Foam quality is calculated by using the following relationship:
Foam quality=(Foam Height−100 mL)/(Foam Height)*100%
Laboratory Results
)
indicates data missing or illegible when filed
SA1 Substituted Acrylamide Polymer—
Below are some graph that simplify the obtained results
The
fluid nucleus
5.2% A1
3.2% A1 +
3.1%
3.1%/A1 +
5.2%
6%
15′
indicates data missing or illegible when filed
indicates data missing or illegible when filed
The hydration level of both polymers plays a very important role for foam stability. Better and more reproducible results are achieved when the polyacrylamide solutions is hydrated for extended period of time prior to adding the G1 guar polymer.
Photos of 3.1 wt % Acrylamide Sodium Acrylate Copolymer and 1 wt % Acrylamide Sodium Acrylate Copolymer illustrate the performance.
Foaming Evaluation with Diutan Gum
Base fluid 3.1 wt % A1+0.21 wt % substituted acrylamide polymer+0.21 wt % Ac+0.5 vol % D
High foam stability with the addition of the Diutan gum. 5 hrs with not drainage observed.
Setting Time of Acrylamide Sodium Acrylate Copolymer when Adding Diutan Gum
No much difference on the setting time with and without Diutan. However, the Diutan impart elasticity on the consistency of the system. The picture with Diutan shows how the bubbles are after the system reaches its hard set time, not fluid drainage.
Evaluation of Surfactants with Diutan Gum and a Acrylamide Sodium Acrylate Copolymer
Composition (Active Components) of Surfactants
A fluid formulated as follows 3.1 wt % Acrylamide Sodium Acrylate Copolymer+0.7 wt % Diutan gum+1.0 vol % Cocamidopropyl Betaine was evaluated further in a circulating foam loop at 100° C. using nitrogen. The hexamethylenetetramine was not included to prevent gelation during the test. The foam was formulated at a quality of 72%. A constant shear rate of 100 s−1 was maintained throughout the test except for three shear ramps where the shear rate was reduced to 75, 50 25 and then increased to 50, 75 and 100 s−1. Table 1 shows the calculated power law parameters, for the foam versus elapsed time. Clearly the foam maintains its viscosity and its shear thinning properties with only minor changes over the test time of 3.5 hours. The rheology trace is included in
Some coarsening of the foam is evident, but the foam has no drainage over the 3.5 hour test time.
The preceding description has been presented with reference to some illustrative embodiments of the Inventors' concept. Persons skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this invention. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.
Furthermore, none of the description in the present application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope: THE SCOPE OF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS. Moreover, none of these claims are intended to invoke paragraph six of 35 USC §112 unless the exact words “means for” are followed by a participle. The claims as filed are intended to be as comprehensive as possible, and NO subject matter is intentionally relinquished, dedicated, or abandoned.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/330,048, filed Apr. 30, 2010, entitled, “Viscosification and Foaming of Polyacrylamides,” and incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61330048 | Apr 2010 | US |
