The Recognition of Mud-Laden Drilling Fluids
With the success of Spindletop, hydraulic rotary drilling became more popular, especially in Texas, Louisiana and in California. There is evidence, however, that hydraulic rotary drilling with mud was also applied successfully in Baku, Azerbaijan prior to Spindletop. Since the use of a mud laden fluid was deemed to be essential for rotary drilling, it is likely that the Baku drillers were using mud. Until the mid to late 1920s the drilling fluid used was just dirt and water. The only additive used was water. Mud-laden drilling fluids were used in both cable tool and hydraulic drilling. In most areas of North America, however, cable tool drilling was still the method of choice.
From 10 to 15 years after Spindletop, the drilling industry began to pay more attenion to drilling fluids. They realized that better control of mud properties lead to better control of drilling costs. The practice was to allow the mud weight and viscosity to naturally increase with the addition of drilled solids. The only control was to dilute the mud, but there were no standard test procedures to guide them on dilution quantities.
Petroleum Division, Bureau of Mines
During the winter of 1912-13, it was noted that an enormous amount of natural gas was being released while drilling for oil in the Cushing oilfield in Oklahoma. Accoring to Lewis and McMurray, appeals were made to the US President and the Secretary of the Interior to examine this situation. In 1913, Heggem and Polard were sent to Oklahoma to examine the drilling operations on Indian lands and to suggest means to eliminate the waste of natural gas. They knew that the use of mud-ladend fluids had been used successfully in California, Texas and Louisianna and determined that it "was the method that would meet meet the situations most efficiently and economically." They published two reports on the use of mud-laden fluids for both cable tools and hydraulic rotary drilling. These reports are described below.
The Bureau of Mines, under the auspices of the Department of the Interior, had established a Petroleum Division to look after all petroleum related operations on government controlled land. In 1914 Congress established that six inspectors were to be employed to look over the oil and gas operations on Indian lands in Oklahoma. These inspectors agreed with the findings of Heggem and Pollard on the use of mud-laden fluids to eliminate natural gas waste. They, however, also included hydraulic roatary drilling in their investigations. The State of OKlahoma in 1915 passed laws for the conservation of oil and gas and concurred with the federal government findings.
Lewis and McMurray wrote bulletin 134 in 1916 summarizing the technical reports and the further investigations that had occured in other parts of the US.. Their bulletin is described below.
Mud drilling fluids were now becomming recognized as essential to successful drilling operations.
Pollard, John Alfred and Heggem, Alfred George 1913. Mud-Laden Fluid Applied to Well Drilling. Technical paper 66, Bureau of Mines.
Pollard and Heggem's purpose, as given to them by the Bureau of Mining, was to "outline a method whereby wells may be drilled without waste of gas." They recognized that the problem was a differential pressure inbalance when using clear water to drill. Although many wells can be drilled with water, in other cases the pressure exerted by clear water was not enough to hold back the formation gas pressure. This inbalance caused a continous loss of natural gas.
The authors also recognized that "clay-laden water" was not new having been used in rotary drilling. But, they state, that this type of fluid was not applied in dry-hole cable tool drilling until 1913. There is documentation, however of the use in 1906 of a circulator system for cable tool drilling in the Coalinga Filed in California. But it was not stated if they used clear water or a mud in that operation.
The following is a synopsis of this 1913 Bureau of Mines Technical Paper No. 66.
The table of contents include:
Description of mud-laden fluid
"In this paper the term mud-laden fluid is applied to a mixture of water with any clay which will remain in suspended in water for a considerable time." They state that places that drill clays called "gumbo" are well suited for making a mud-laden fluid. They also recommend against using drillings if they contain sand. They state the proportion of clay to acheive the best results should be about 20%.
The action of mud-laden fluid on porous formations
Pollard and Heggem recognized that the mud-laden fluid was forced into the formation like "muddy water going through a filter." They described the process perameters of differential pressure and porosity of the formation. They did not recognize a filter cake, but desribed the process as "the fluid enetrs the porous stratum for a short distance and deposits clay that that clogs the openings ..."
Preparing mud-laden fluid
The following are Pollard and Heggem’s recommendations for mud preparation
Slush pit – 15 or 20 feet long, 10 feet wide and 3 feet deep dug close to the derrick
Care should be taken not to mix with this fluid any material that will not stay in suspension
Mud pump – duplex slush pump
The following diagram shows their recommendation for on-site preparation of a mud-laden fluid.
The rest of the report is concerned with the operational aspects of cable tool drilling with fluid in the hole. The Topics covered are:
Heggem, Alfred George and Pollard, John Alfred 1914. Drilling Wells in Oklahoma by the Mud-Laden Fluid Method. Technical paper 68, Bureau of Mines.
The use of a mud-laden fluid for cable tool operations was first documented in 1913 by the authors as described above. This document was a report instigated by the Department of the Interior, Bureau of Mines to study the dry hole cable tool drilling in Oklahoma that resulted in the waste of natural gas while exploring for oil. From their study of mud-laden fluid, they purposed to test and demonstrate the adaption of rotary drilling clay and water fluids for use in dry hole drilling to minimize waste gas..
Their demonstration was successful. The technical report was strickly on the mechanics of drilling the hole. No mention was made of preparing the mud, only that they recommended a clay-laden fluid be used.
The mud-laden fluid part of their summary included:
Lewis, James O. and McMurray, William F. 1916. The Use of Mud-Laden Fluid in OIl and Gas Wells. Bulletin 134 Bureau of Mines.
The technical papers described above caused so much interest in mud-laden fluids that copies of the papers were nearly gone within two years. Instead of reprinting the papers, the Petroleum Division decided replace them with this document using some data from the papers augmented by additional investigations. This bulletin covers dry cable tool drilling, cable tool mud circuation and hydraulic rotary drilling.
Description of Mud-Laden Fluid
The initial description of a mud-laden fluid is the same as proposed by Pollard and Heggem. "In this bulletin the term "mud-laden fluid" is appled to a mixture of water and any clayey material which will remain suspended in water for a considerable time and is free fron sand, lime cuttings or similar materials."
This document, however, expands on the definition by describing the consistency of the fluid. This consistency description is repoduced below.
"The consistency of the fluid should be varied according to the conditions for which it is employed. Most frequently mixtureswith a specific gravity 0f 1.05 to 1.15 are used in drilling - that is, 5 to 15 per cent heavier than water. When the fluid is not used to drill in, thicker fluid is often employed, which has the advantages of greater weight and clogging up the pore more readily. Experience soon enables the operator to judge the consistency of fluid required for practical purposes."
Variation in fluid prepared from different clays or shales
Lewis and McMurray recognized the great variations that can arise using locally provided clays or drillied solids in mud preparation. They stated:
"There is considerable variation in the nature of fluids derived from different clays or shales. When the same volumes of two different materials are mixed with the same volumes of water the resulting fluids may differ considerably in specific gravity, or of two fluids of the same specific gravity one may be more viscous or thicker than the other."
To try to differentiate among the clays used they ran a set of experiments observing particle settling in different muds collected from various wells. The results, however, did not show clay differences , but only looked at how various specific gravity fluids behaved. There conclusion was that lighter fluids settle slower that heavier fluids. No doubt representing the higher viscosities in th eheavier muds. Their conclusions were that "it is advisable to use a heavy fluid that will very settle little" and that a "mud fluid, properly mixed and employed, does not solidify behind the casing, even in deep wells and after long periods."
Disadvantages of Using Clear Water
Lewis and McMurray were definately against the use of clear water in cable tool drilling, as shown in the following quote.
"Some drillers contend that clear water should have the same effect as the mud-laden fluid, but experience has shown that it does not. Many wells cannot be filled with clear water, because the water continues to flow into the sand indefinately with no clogging effect and consequiently does not rise high enough in the well to give sufficient pressure to overcome that of the gas. Moreover, the action of the water on the walls of the hole causes caving, and an attempt to use clear water in a well invites trouble and may injure the producing sands.
Preparing the Mud-Laden Fluid
This document expanded on the Pollard and Heggem preperation method as follows.
1 They recommend using clays from nearby or from material derived from drillings
2 . Use a 300 bbl slush pit, constructed close to the rig
3 Drillings from sandstones and limestones should not be used
4 . A few hours time using unskilled labor is required to prepare the slush pit.
5 Sttling out of sand, limestone cuttings, etc., is necessary in order to avoid freezing of casing and of tools
The document provides a "ground plan of equipment and used in handling mud-laden fluids and a schematic that shows a device for circulating mud fluid in the well."