Gas-producing Zones Research Articles

Delaware Basin Cementing - Problems and Solutions

Abstract Increasing drilling activity in the ultra deep horizons of the Delaware basin has focused intense interest on developing effective cementing practices for the problems encountered in this area. Probably the most critical decision facing the drilling engineer is proper selection of casing points to cope with the alternating lost circulation and high pressure gas zones common to the basin. Although the lithology of different areas in the basin is very similar, important differences do exist, and must be recognized to effectively cement these casing strings. The use of formation fracture gradients as an index of design limits has proven to be one of the most effective ways of anticipating the changes required in cementing programs. Gradient profiles of several fields are listed to illustrate the different cementing designs required by seemingly minor changes in lithology. Correct determination and tabulation of gradient profiles has been a significant factor in designing cement placements throughout this area. In general, cementing practice has been influenced by four predominant problems: attempting to cement long annular spaces across weak, incompetent formations; high pressure gas zones that can be drilled with light muds due to limited permeability but are not under complete control during cementing; wide temperature differences between top and bottom of long cement columns; and extremely long liners set in small hole across weak formations. The design of cementing programs to cope with these problems has been an interesting and informative evolution that is followed from the first few wells through present practice. Introduction Probably the most important decision facing the drilling engineer on Delaware basin wells is the selection of casing points. When casing points have been chosen, the next problem is designing an effective cementing program. An accurate analysis of existing hole conditions and correspondingly correct cement design are imperative for successful drilling operations. Making these analyses and correctly predicting cement slurry behavior have been significant factors in reducing drilling costs. Development of the data and analytical techniques to provide this control has been interesting. The first wells drilled in the basin were cemented largely by techniques and procedures used in other fields. Most of the mud weights used were too light to provide an index of cement density limits. Analysis of the results indicated that changes should be made in cementing the succeeding well. This approach is effective, although expensive, in a given field and will finally progress to a successful cementing program so long as formation conditions remain constant. Unfortunately, formation conditions in the Delaware basin are not known for their consistency. Although lithology appears very similar in many wells throughout the basin, important differences do exist. Recognizing and interpreting the effect of these formation changes have determined the success of cementing design in this area. History The first wells drilled in the Delaware basin employed casing programs different from those presently used. A brief resume of these earlier programs will illustrate the importance of selecting effective casing points. Surface casing was set through the fresh-water beds and Rustler dolomite. Intermediate casing was set just above the Delaware sand, covering shale, salt and anhydrite sections. The second intermediate casing was set through the Delaware members and Bone Spring into the top of the Wolfcamp. Another string was required when the Mississippian was topped to shut off Wolfcamp and Pennsylvanian gas. In the Rojo Caballos field casing had to be set just above the Penn and again immediately below it.1 Drilling was then continued to the top of the Ellenburger where another string was set. After the Ellenburger was drilled to total depth, a production liner was set or the well completed open hole. These programs required five strings of casing and six if a production liner was set. Cementing these casings presented problems, but probably not so severe as those in recent practice. Open intervals were shorter and formation extremes were not so wide. Sections prone to lost circulation were drilled and casing set or gas producing zones were isolated, so these two types of formations were not drilled together in one casing interval.

Gas Producing Zones of Greenbrier (Mississippian) Limestone, Southern West Virginia and Eastern Kentucky

The Mississippian Greenbrier limestone, in southern West Virginia and eastern Kentucky, consists of interbedded layers of clastic and non-clastic limestone. In the area of investigation, it ranges from only a few feet to 1,200 feet in thickness. Oil and gas of the Greenbrier limestone has been obtained from porosity in (1) oolitic zones, (2) dolomite zones, and (3) zones of oolitic, dolomitic, sandy limestone. Zones of oolitic limestone are common in the lower part of the Greenbrier limestone, especially near the lower limit of the formation. The oolites were apparently developed in shallow water near the shoreline at the extreme margins of the Greenbrier basin. The development of basal oolitic zones is most strongly governed by the topographic features existing on the pre-Greenbrier erosional surface of the underlying Maccrady Formation. The basal oolitic zones are elongate in a direction parallel with the ancient shoreline which is, in turn, parallel with the isopach contours drawn on the total thickness of the Greenbrier l mestone. The uppermost members of the Greenbrier limestone are time-equivalent and apparently were deposited contemporaneously over an extensive area in southern West Virginia and eastern Kentucky. The clastic and dolomitic zone at or near the base of the Greenbrier limestone crosses time lines and becomes progressively older toward the axis of the basin of deposition. The presence of hydrocarbons within the oolitic zones soon after deposition may have prevented their complete cementation by excluding mineralized solutions from the available interstitial porosity within the sediments.

Gas Occurrence in Piceance Basin, Colorado: ABSTRACT

Mostly gas is produced in the Piceance basin of western Colorado. The basin, containing about 4,000 square miles, is well defined by the Tertiary-Cretaceous outcrop contact beyond which are the surrounding elevated areas. The basin is in the early stages of development with a density of only one well for every 25 square miles. The lack of pipeline outlet prior to 1956 resulted in slow development but now three pipelines serve the area and drilling activity has been at an accelerated pace. Of the total wells drilled, approximately one half are capable of producing gas from the Tertiary and upper Cretaceous rocks. Due to the thickness of the section, 22,000 feet to the basement, only six wells have tested the pre-upper Cretaceous section. Most accumulations of gas are due to stratigraphic traps. The paucity of subsurface data is the cause for the present disagreement among geologists of the stratigraphy and geologic history. Tentative correlations from the outcrops on the periphery of the basin are carried across the basin, particularly of the Mesaverde and upper Mancos beds, with a discussion of how the depositional history complicates the problem. The development history which includes the identification of the multiple gas-producing zones indicates that this basin will become one of the important gas-producing areas of the Rocky Mountains. End_of_Article - Last_Page 415------------

High Strength Granular Sealing Material Increases Efficiency of Primary Cementing and Squeeze Cementing

Abstract The use of high strength granular materials in cement slurries has proved beneficial for cementing casing and squeeze cementing operations in Permian in Basin oil and gas wells. The addition of 1 to 4 lb of ground walnut shells to each sack of cement made possible successful high column cementing jobs in fields where high fill-ups normally cannot be obtained because of lost circulation. In squeeze cementing operations the number of cementing stages required for shutting off water was reduced by the addition of walnut shells to the last 50 per cent of the volume of cement slurry. Introduction The high hydrostatic head, created in the annulus when cementing casing, frequently is the cause of loss of slurry into weak formations or formations containing fractures or vugs. Common precautions taken to reduce this loss are reducing the density of the slurry adding effective sealing agents to the slurry, or both. One phase of this paper concerns the use of high strength granular sealing materials in cement slurry to seal openings into formations so that the slurry may be pumped to the desired level behind the casing. In squeeze cementing operations neat cement often fails to effect a complete seal because of the tendency of the slurry to enter only the weakest zones. This is indicated by the number of stages frequently required to stop the flow of water or gas. The intrusion of cement slurry into each perforation in a water or gas producing zone is probably necessary to eliminate flow completely, and a high final squeeze pressure may be a means of assuring entry of cement into each perforation or zone of weakness. The second phase of this paper concerns the use of high strength granular materials in cement slurries to obtain a high final squeeze pressure.

Developments in Arkansas and North Louisiana in 1948

Wells drilled during 1948 in Arkansas and North Louisiana totaled 1,811. In 1947, 1,343 wells were drilled. This is a 35 per cent increase in drilling activity. The 1947 total was 34 per cent greater than in 1946. There were 220 wildcats drilled in 1948; of this total, 106 were drilled in Arkansas and 114 in north Louisiana. In 1947, 237 were drilled; of this number, 76 were in Arkansas and 161 in North Louisiana. The decrease in wildcatting in 1948 was 7½ per cent. For the past several years the percentage increase in wildcatting and total wells drilled have been approximately the same. Much of the increase in total wells drilled in 1948 was due to heavy drilling in old shallow fields such as the Caddo field in Caddo Parish, Louisiana, which increased form 306 producing wells drilled in 1947 to 718 wells in 1948. In Arkansas 4 new oil fields were discovered. No new gas or distillate fields were found. In addition 7 new oil zones in old fields were added. No new gas or distillate producing zones were discovered. In North Louisiana 3 new oil fields, 1 new distillate field, and 4 new gas fields were discovered. Three new oil zones, 9 new distillate zones, and 2 new gas zones were added to existing fields. New fields and new producing zones in old fields totaled 33 for the are in 1948. There were 35 in 1947. Geophysical activity in Arkansas totaled 774 crew weeks, of which the seismograph contributed 426 weeks, the gravity meter 109 weeks, the magnetometer 112 weeks, and the core drill 127 weeks. In North Louisiana crew weeks totaled 1,236, of which 953 were contribute by the seismograph, 216 by the gravity meter, and 67 by the core drill. There were no magnetometer crews reported in North Louisiana. In the area total crew weeks of geophysical activity were 1,986 in 1947; this is comparable with 2,010 in 1948.

Developments in Arkansas and North Louisiana in 1946

In all, 1,000 wells were drilled in the area in 1946. This is a 45% increase in drilling activity over the 1945 total of 692 wells. One hundred seventy-two wildcats were drilled, of which 55 were in Arkansas and 117 in North Louisiana. This is comparable with 34 in Arkansas and 81 in North Louisiana in 1945. Wildcatting thus increased by 50%. In Arkansas 5 new oil fields and 9 new oil-producing zones in old fields were discovered. North Louisiana had 5 new oil fields, 1 new gas field, 2 new distillate fields, 2 new oil-producing zones in old fields, 1 new gas-producing zone in an old field, and 1 new distillate producing zone in an old field. This is a total of 26 new discoveries. Subsurface work led to most of the new discoveries. In Arkansas and North Louisiana 61,642,142 barrels of crude oil were produced. This is an increase of 7,372,472 barrels over 1945 figures. Geophysical activity in Arkansas totaled 470 crew weeks, with the seismograph contributing 333 crew weeks to the total. In North Louisiana crew weeks totaled 1,779, with the seismograph contributing 913 and the gravity meter 859 crew weeks.

Developments in East Texas During 1945

One new oil-producing area and four new gas-producing areas were discovered in East Texas during 1945. The LaRue area in Henderson County produces oil from the Bacon limestone member of the Rodessa section. The gas-producing areas include Stony Point in Freestone County and Marshall in Harrison County, both of which produce from the Pettit section; Fairfield in Freestone County which produces from the Woodbine and Travis Peak, and Whelan in Harrison County which produces from the Rodessa and Travis Peak. Deeper drilling in old fields resulted in the discovery of new oil-producing zones in two fields and new gas-producing zones in two additional fields. Shallow oil was found and produced in two old fields. Exploratory drilling in East Texas was again characterized by deeper tests having the Paluxy, lower Glen Rose, Travis Peak, Cotton Valley, and Smackover formations as their principal objectives. Woodbine exploration was extended into the southern part of the East Texas area.

Developments in South Arkansas and North Louisiana in 1945

A total of 692 wells comprised the drilling operations in South Arkansas and North Louisiana for the year 1945, as compared with 547 in the preceding year and 602 in 1943. Of this total for 1945, 115 dry wildcats were drilled, of which 34 were drilled in South Arkansas and 81 in North Louisiana, as compared with 64 wildcats in South Arkansas and 79 in North Louisiana for 1944. South Arkansas claimed 3 new oil fields and 3 new producing zones in old fields, while North Louisiana was credited with 7 new oil fields, 4 new gas fields, 1 new distillate field, 4 new oil-producing zones in old fields, 3 new gas-producing zones in old fields, and 1 new distillate-producing zone in old fields. Future drilling might prove several oil pools, which have been given new oil-pool rank, to be extensions of old pools. The gross oil production of South Arkansas during 1945 amounted to 28,547,400 barrels as compared with 29,312,020 barrels in the preceding year. North Louisiana produced 25,722,270 barrels of oil in 1945 and 26,569,565 barrels in 1944. The area as a whole showed a decline in production of oil of approximately 2.9 per cent. Subsurface data led to the discovery of more new oil and gas pools than any other method employed, with seismograph a close second.

Oil-Field Waters of Montana Plains

Tabular and graphic analyses of waters from the oil- and gas-producing zones of Montana are presented and discussed. Montana group waters, with the exception of those waters associated with gas, are dilute to moderately dilute solutions of sodium salts, sulphate being present in many waters to a considerable extent. Colorado group waters in the Sweetgrass arch fields are moderately concentrated to concentrated solutions of sodium chloride; elsewhere these waters are less saline and moderately dilute. Kootenai waters resemble Colorado waters to some extent, but are ordinarily more alkaline. Ellis waters are alkaline, moderately concentrated, and contain hydrogen sulphide in appreciable amounts. The Quadrant formation yields large flows of water in which the sulphates of calcium and magnesium dominate the chemical system. Tensleep waters of central and southern Montana are similar to Quadrant wate s of north-central Montana. Madison waters of primary characteristics are found in the Sweetgrass arch fields, and secondary characteristics are present in the Madison waters of the north-central and central fields. The analyses indicate that all the oil- and gas-field waters of Montana have been considerably modified by the infiltration of meteoric waters.

Notes on the Structural History and Oil Possibilities of the Dakota Basin: ABSTRACT

This article contains a structure map contoured on the top of the Dakota sandstone. The periods of tilting and folding are discussed along with the evidence for these structural deformations. Three cross sections are included to explain the structure and geologic history. Paleogeologic maps for the pre-Cretaceous and pre-Pennsylvanian surfaces are shown. The possible oil- and gas-producing zones of the Dakotas are discussed and compared with sands that are producing oil or gas in the surrounding states. End_of_Article - Last_Page 911------------

Oil-Field Waters of Wyoming and Their Relation to Geological Formations

Tabular and graphic analyses of waters from the oil- and gas-producing zones of Wyoming are presented and discussed. Post-Chugwater waters are essentially solutions or sodium salts, whereas in pre-Chugwater waters calcium and magnesium sulphates ordinarily predominate. Frontier waters are solutions of sodium chloride and sodium bicarbonate in varying proportions. Waters from the Dakota group are solutions of sodium salts, but contain appreciable quantities of sulphate. Most Sundance waters are solutions of sodium salts similar, except for concentration, to Frontier and Dakota group waters. Chugwater water is exceptionally concentrated, ranging from 30,000 to 50,000 parts per million. Embar waters contain hydrogen sulphide and are the youngest subsurface waters in which secondary salinity is prominent. In most of the Tensleep waters secondary characteristics dominate the chemical system with secondary salinity ordinarily occupying 40-70 per cent. Madison waters commonly have a somewhat higher secondary salinity than Tensleep waters in the same ar a, but otherwise resemble them. The analyses indicate that all the oil-field waters of Wyoming have been considerably modified by the infiltration of surface water.