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Synthesis and evaluation of a novel cross-linked fluid loss additive for oil-based mud.


OBMs are specially selected to drill complex wells because of high performances, including high shale inhibition, good lubricity, thermal and chemical stability. In order to enhance well productivity, OBMs are often used to drill long open hole reservoir. During these operations, when the fluids come in contact with the reservoir, fluid losses may occur. This can not only increase E&P costs but also reduce formation permeability which is detrimental for the oil-well productivity.

One of desired properties for muds is the minimum fluid loss volume which can be achieved by formation of a low-permeability filter cake on the wellbore. Fluid loss and filter cake properties could influence wellbore stability, differential sticking, formation damage and other aspects. As a result, filtration control is important for both drilling performance and well productivity [1-3].

Various kinds of fluid loss additives have been developed in last decades, such as Gilsonite, organic lignite, epoxidized cardanol derivative[4], metallic soap [5], modified tannin [6] and oil swell elastomer [7], etc. The modified humic acid was found to be cost-effective and exhibit good performance, so it attracted more and more attention recently. However, there are a lot of disadvantages for existing technology, for example, a huge amount of water should be removed after reaction, organ[degree]Clay or other dispersants should be added, and so on.

On this background, a novel cross-linked fluid loss additive (SDFL) was developed by altering the wettability of humic acid with fatty amine and appropriate crosslinking agent.

Experimental Materials and Methods


Commercial lignites were obtained from Chuangxin Science Technology Co. Ltd, in Shandong Province, China. Fatty acid, polyalkylene polyamine and crosslinking agent were provided by Shengli Chemical Co. Ltd. Fluid loss additives, including modified lignite 1#, 2#, and modified rosin, oil-soluble fiber and Gilsonite, were provided by Shengli Drilling Mud Company.

Synthesis of SDFL

A certain amount of white oil was mixed with 1.5 mole polyamine in a kneading machine and heated to 155-165 [degree]C. Then, 400 g of humic acid was added into the solution. After stirring for 30 min, appropriate amount of crosslinking agent was added. After 2 h, the product was removed, dried at 100 [degree]C and ground.

FTIR Characterization of SDFL

0.2 g of KBr was ground to a fine powder and then intensively mixed with 1-2 mg SDFL. The mixture was pressed and its chemical structure was determined through a NEXUS FT-IR spectrometer (Thermo Nicolet Corporation), scanning from 4000 to 400 [cm.sup.-1], with a 4 [cm.sup.-1] resolution in transmission.

Evaluation of SDFL

Mud Formulation

The tested formulas of the OBMs at 1.1g/[cm.sup.3] with an Oil/Water ratio of 80/20 are shown in Table 1 below.

The effect of crosslinking agent content on the effectiveness of SDFL

The filtration properties of SDFL samples with different crosslinking degrees were measured in muds after hot-rolled at 150[degree]C for 16h.

The effect of the concentration of SDFL on the fluid loss for the base mud

The base muds with different concentrations of SDFL were hot-rolled under 150, 180, 200 [degree]C for 16h, respectively. The fluid losses were taken at 150 [degree]C and 3.5MPa.

Comparison test

Mud systems were prepared using SDFL and other fluid loss additives. Prepared muds were subjected to standard testing, such as filtration and rheological properties, and electric stability, after hot-rolled at 150 [degree]C for 16h.

Anti-contamination evaluation of OBMs

To further establish the effectiveness of SDFL, contamination studies were performed on the base muds where the effect of contamination of 5%, 10%, 15%, 20% drill solids and 5%, 10%, 15% of 20% CaCl2 brine were measured respectively. After hot rolling at 150[degree]C for 16h, these contaminated mud systems were determined for the filtration and rheological properties.

Results and Discussion

IR characterization of SDFL

Fig. 1 illustrated the IR spectra of humic acid (HA) and SDFL. Compared to HA, the reduction in absorption band around 1705 [cm.sup.-1] (-COOH group) indicated the reaction occurred between -COOH and -N[H.sub.2] groups and this was further proved by the appearance of new absorption band around 1649 [cm.sup.-1] (-CONH-). The presence of absorption bands around 2922 [cm.sup.-1] (-C[H.sub.3]) and 2854 [cm.sup.-1] (- C[H.sub.2]-) showed that the humic acid has been successfully grafted with long alkyl chain. However, due to the low concentration of the crosslinking agent, its absorption band could not be detected.


The effect of crosslinking agent content on the effectiveness of SDFL

The relationship between cross-linking degree and the HTHP filtration control property of SDFL was investigated. The molecular weight of SDFL changed with the content variation of the crosslinking agent, leading to different filtration behavior of SDFL. As shown in Figure 2, when the content of the crosslinking agent is 0.3%, the fluid loss for the mud system (28 g/[cm.sup.3] SDFL) reduced dramatically. Until the content of crosslinking agent reached 0.45%, wherein the SDFL had an optimum crosslinking density and molecular weight, the minimum fluid loss was obtained. Further increasing the content of the crosslinking agent, however, SDFL showed poor performance.


The effect of the concentration of SDFL on the fluid loss for the base mud

As illustrated in figure 3, SDFL gave an efficient filtration control property, addition of 14 g/[cm.sup.3] SDFL can reduce the fluid loss from 36 mL down to 6.4 mL after hot-rolling at 150 [degree]C. Although hot-rolling at 200 [degree]C led to the increase in the fluid loss for 14 g/[cm.sup.3] SDFL-treated base mud, the fluid loss value was 11mL still satisfying the requirements of high-temperature drilling operation[9]. Furthermore, increasing the concentration of SDFL up to 42 g/[cm.sup.3] can keep the fluid loss at a low level of about 5 mL for the mud hot-rolled at 200 [degree]C.


Comparison of SDFL and other FLA

To assess the performance of SDFL, five other fluid loss additives in use were tested as shown in Table 2.

As shown in Table 2, SDFL exhibited superior performance over the investigated products and could reduce fluid loss value by 86%. Furthermore, the addition of SDFL into OBM led to no free water in filtrate, thinner filter cake, and slightly higher electrical stability. Gilsonite is unacceptable to environment and contributes to the slight increase in the viscosity and less electrical stability of OBM.

Other two same types of fluid loss addive, modified 1# and 2#, gave less effecient filtration control, thicker filter cake and lower electrical stability than SDFL. Moreover, these two modified lignits had significant effect on the rheological of the base mud.

In contrast to outstanding filtration property of SDFL, modified rosin introduced significant increase in the fluid loss and formed a filtercake with a poor quality. Note also that a dramatic increase in viscosity of the OBM was observed with the additon of the oil soluble fiber.

Anti-contamination test

During drilling operation, the phenomena such as the drill solids cumulated and the brine influx encountered, the filtration properties of OBM may be deteriorated. So it is necessary to investigate the anti-contamination ability of SDFL against drill solids and brine water.

As shown in Table 3, the contamination of drill solids caused slightly deterioration of filtration properties. This is to be expected because the increasing fraction of poorly dispersed drill solids in filter cake can make the filter cake thicker and less compacted, leading the filtrate to easily flow through the filter cake. Although there was an increase in viscosity and yield point, filtration properties were still satisfactory.

Table 4 shows the effect of brine contamination on the rheological and filtration properties of OBMs. Increasing brine content contributed to the increase in brine droplets number and friction between them inducing overall increase in rheological profile. The brine contamination also induced the decrease in electrical stability by about 300V, but the mud systems remained electrical stable. In addition, the SDFL treated muds exhibited more excellent filtration control performance: possibly due to much more bridged and deformed brine droplets incorporated into muds.


A novel fluid loss additive (SDFL) has been developed. Moderate crosslinking resulted in better control of SDFL properties. Laboratory tests demonstrated that SDFL was thermal stable at temperatures as high as 200 [degree]C. The test data indicated that SDFL performed better than Gilsonite and other fluid loss additives and had less effect on the rheological properties of base mud. Furthermore, OBM treated with SDFL maintains excellent filtration control properties even in the presence of drill solids and brine.


We would like to thank the financial support provided by NSFC(41072094) for this project.


[1] Aston, M., Mihalik, P., Clarke, Tunbridge, S., 2002, "Towards zero fluid loss based muds," SPE Annual Technical Conference and Exhibition, San Antonio, Texas, September 29-[degree]Ctober 2, SPE Paper no. 77446, pp. 1-9.

[2] Herzhaft, Benjamin, Audibert-Hayet, Annie, Sandford, Rick, Freche, Patrick, 2001, "Optimization of SBM formulations for minimum damage," 2001 International Symposium on Oilfield Chemistry, Houston, Texas, February 1316. SPE Paper no. 64981, pp. 1-7.

[3] Oleas, Andres, Osuji, Collins E., Chenevert, Martin E., Sharma, Mukul M., 2008, "Entrance pressure of oil based mud into shale: effect of shale, water activity, and mud properties," 2008 SPE Annual Technical Conference and Exhibition, Denver, Colarade, USA, Spetember 21-24, SPE Paper no. 116364, pp. 1-19.

[4] Ballard, David, Anthony, 2008, "Hydrophobically modified fluid loss additives and viscosifier products," WO 2008/123888.

[5] Miller, Jeffrey J., 2007, "Metallic soaps of modified fatty acids and rosin acids and methods of making and using same," U.S. Pat. No. 2007/0259790/A1.

[6] Patel, Arvind D., Mettath, Sashikumar, Stamatakis, Emannuel, Young, Steve, Friedheim, Jim, 2008, "Fluid loss additive for oil-based muds," U.S. Pat. No. 2008009421A1.

[7] Van de Peer, Dirk, D'Haese, Francois Cyriel, Dams, Rudolf J., 2010, "Additive to reduce fluid loss for drilling fluids," U.S. Pat. No. 2010/0173804 A1.

[8] Hanssen, Jan Erik, Jiang Ping, Haga, Marton, et al, 1999, "Oil-based reservoir drilling fluid for critical field cases: integrated formation-damage evaluation and system development," SPE European formation damage conference, Hague, Netherlands, May 31 - June 1, SPE Paper no. 54732, pp. 1-12.

[9] Shu fuchang, Shi maoyong, Xiang xingjin, 2008, "Study on synthesis of fluid loss reducer for oil-based drilling fluid by modifying humic acid," Applied Chemical Industry, 37(9), pp. 1067-1069.

Ping FENG, Zhengsong QIU and Jie CAO

School of Petroleum Engineering, China University of Petroleum (East China), No. 66, Changjiang West Road, Qingdao 266580, China
Table 1: Compositions of oil-based muds

Components Base mud Base mud + SDFL

Base oil (mL) 240 240
Primary emulsifier (kg/[m.sup.3]) 20 20
Lime (kg/[m.sup.3]) 17 17
20% Ca[Cl.sub.2] solution(mL) 60 60
Secondary emulsifier (kg/[m.sup.3]) 10 10
Wetting agent (kg/[m.sup.3]) 20 20
Organoclay (kg/[m.sup.3]) 10 10
Fluid loss additive (kg/[m.sup.3]) 0 28
Barium sulfate (g) 125 125

Table 2: Rheological and filtration properties of 1.1g/[cm.sup.3]
base mud with 28 g/[cm.sup.3] SDFL or other fluid loss additives

FLA Rheological properties
 (mPa-s) (mPa-s) (Pa)

Base mud 26.0 22.5 3.5
SDFL 28.0 24.5 3.5
Modified 40.0 36.0 4.0
lignite 1#
Modified 34.5 32.0 2.5
lignite 2#
Modified 31.0 28.0 3.0
Oil-soluble 70.0 50.0 20.0
Gilsonite 31.5 28.5 3.0

FLA Filtration properties Electrical
 HTHP Free Filter stability (V)
 FL (mL) water cake
 (mL) thickness
Base mud 36.0 1.0 7.0 1760
SDFL 5.0 0 2.5 1900
Modified 9.6 0 4.0 1640
lignite 1#
Modified 18 1.0 5.5 1800
lignite 2#
Modified 59 9.0 10.0 1820
Oil-soluble 16 2.4 2.0 >2000
Gilsonite 5.4 0 2.5 1580

Table 3: Rheological and filtration properties of 1.1g/[cm.sup.3]
mud containing 28 g/[cm.sup.3] SDFL with different contents of
drill solids

Drill solid Rheological properties Filtration properties
(%) AV PV YP HTHP Free Filter
 (mPa-s) (mPa-s) (Pa) FL water cake
 (mL) (mL) thickness

0 26.0 22.5 3.5 5.0 0 2.5
5 29.5 25.0 4.5 6.4 0 3.0
10 38.0 33.0 5.0 6.8 0 3.5
15 39.5 34.0 5.5 6.8 0 3.5
20 38.5 33.0 5.6 7.0 0 3.5

Table 4: Rheological and filtration properties of 1.1g/[cm.sup.3]
mud containing 28 g/[cm.sup.3] SDFL with additional contents of
20% Ca[Cl.sub.2] aqueous solution

20% Rheological properties
Ca[Cl.sub.2] AV PV YP
solution (%) (mPa-s) (mPa-s) (Pa)

0 26.0 22.5 3.5
5 31.5 26.5 5.0
10 37.5 32.0 5.5
15 42.0 36.5 5.5

20% Filtration properties Electrical
Ca[Cl.sub.2] HTHP Free Filter stability
solution (%) FL water cake (V)
 (mL) (mL) thickness

0 5.0 0 2.5 >2000
5 4.4 0 2.0 1953
10 3.0 0 2.0 1810
15 2.2 0 1.6 1706
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Author:Feng, Ping; Qiu, Zhengsong; Cao, Jie
Publication:International Journal of Petroleum Science and Technology
Date:Sep 1, 2012
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